diff --git a/src/region_cylinder.cpp b/src/region_cylinder.cpp
index d6d71ba9b9..b806ea07ea 100644
--- a/src/region_cylinder.cpp
+++ b/src/region_cylinder.cpp
@@ -15,12 +15,16 @@
 #include "stdlib.h"
 #include "string.h"
 #include "region_cylinder.h"
+#include "update.h"
 #include "domain.h"
+#include "input.h"
+#include "variable.h"
 #include "error.h"
 
 using namespace LAMMPS_NS;
 
 #define BIG 1.0e20
+enum{CONSTANT,VARIABLE};
 
 /* ---------------------------------------------------------------------- */
 
@@ -36,15 +40,29 @@ RegCylinder::RegCylinder(LAMMPS *lmp, int narg, char **arg) :
   if (axis == 'x') {
     c1 = yscale*atof(arg[3]);
     c2 = zscale*atof(arg[4]);
-    radius = yscale*atof(arg[5]);
   } else if (axis == 'y') {
     c1 = xscale*atof(arg[3]);
     c2 = zscale*atof(arg[4]);
-    radius = xscale*atof(arg[5]);
   } else if (axis == 'z') {
     c1 = xscale*atof(arg[3]);
     c2 = yscale*atof(arg[4]);
-    radius = xscale*atof(arg[5]);
+  }
+
+  rstr = NULL;
+  if (strstr(arg[5],"v_") == arg[5]) {
+    int n = strlen(&arg[5][2]) + 1;
+    rstr = new char[n];
+    strcpy(rstr,&arg[5][2]);
+    radius = 0.0;
+    rstyle = VARIABLE;
+    varshape = 1;
+    variable_check();
+    shape_update();
+  } else {
+    radius = atof(arg[5]);
+    if (axis == 'x') radius *= xscale;
+    else radius *= xscale;
+    rstyle = CONSTANT;
   }
 
   if (strcmp(arg[6],"INF") == 0 || strcmp(arg[6],"EDGE") == 0) {
@@ -100,6 +118,7 @@ RegCylinder::RegCylinder(LAMMPS *lmp, int narg, char **arg) :
   if (radius <= 0.0) error->all(FLERR,"Illegal region cylinder command");
 
   // extent of cylinder
+  // for variable radius, uses initial radius
 
   if (interior) {
     bboxflag = 1;
@@ -139,9 +158,18 @@ RegCylinder::RegCylinder(LAMMPS *lmp, int narg, char **arg) :
 
 RegCylinder::~RegCylinder()
 {
+  delete [] rstr;
   delete [] contact;
 }
 
+/* ---------------------------------------------------------------------- */
+
+void RegCylinder::init()
+{
+  Region::init();
+  if (rstr) variable_check();
+}
+
 /* ----------------------------------------------------------------------
    inside = 1 if x,y,z is inside or on surface
    inside = 0 if x,y,z is outside and not on surface
@@ -400,3 +428,29 @@ int RegCylinder::surface_exterior(double *x, double cutoff)
     return 0;
   }
 }
+
+/* ----------------------------------------------------------------------
+   change region shape via variable evaluation
+------------------------------------------------------------------------- */
+
+void RegCylinder::shape_update()
+{
+  radius = input->variable->compute_equal(rvar);
+  if (radius < 0.0)
+    error->one(FLERR,"Variable evaluation in region gave bad value");
+  if (axis == 'x') radius *= xscale;
+  else radius *= xscale;
+}
+
+/* ----------------------------------------------------------------------
+   error check on existence of variable
+------------------------------------------------------------------------- */
+
+void RegCylinder::variable_check()
+{
+  rvar = input->variable->find(rstr);
+  if (rvar < 0)
+    error->all(FLERR,"Variable name for region cylinder does not exist");
+  if (!input->variable->equalstyle(rvar))
+    error->all(FLERR,"Variable for region cylinder is invalid style");
+}
diff --git a/src/region_cylinder.h b/src/region_cylinder.h
index 93bb74aaff..07c26ca065 100644
--- a/src/region_cylinder.h
+++ b/src/region_cylinder.h
@@ -30,15 +30,22 @@ class RegCylinder : public Region {
  public:
   RegCylinder(class LAMMPS *, int, char **);
   ~RegCylinder();
+  void init();
   int inside(double, double, double);
   int surface_interior(double *, double);
   int surface_exterior(double *, double);
+  void shape_update();
 
  private:
   char axis;
   double c1,c2;
   double radius;
   double lo,hi;
+  int rstyle,rvar;
+  char *rstr;
+
+  void variable_check();
+
 };
 
 }
diff --git a/src/region_sphere.cpp b/src/region_sphere.cpp
index 773fc4cb16..28436cc171 100644
--- a/src/region_sphere.cpp
+++ b/src/region_sphere.cpp
@@ -15,9 +15,9 @@
 #include "stdlib.h"
 #include "string.h"
 #include "region_sphere.h"
+#include "update.h"
 #include "input.h"
 #include "variable.h"
-#include "update.h"
 #include "error.h"
 
 using namespace LAMMPS_NS;
@@ -43,14 +43,19 @@ RegSphere::RegSphere(LAMMPS *lmp, int narg, char **arg) :
     radius = 0.0;
     rstyle = VARIABLE;
     varshape = 1;
+    variable_check();
+    shape_update();
   } else {
     radius = xscale*atof(arg[5]);
     rstyle = CONSTANT;
   }
 
+  // error check
+
   if (radius < 0.0) error->all(FLERR,"Illegal region sphere command");
 
-  // extent of sphere, will be 0.0 for variable radius
+  // extent of sphere
+  // for variable radius, uses initial radius
 
   if (interior) {
     bboxflag = 1;
@@ -79,16 +84,7 @@ RegSphere::~RegSphere()
 void RegSphere::init()
 {
   Region::init();
-
-  // check variable
-
-  if (rstr) {
-    rvar = input->variable->find(rstr);
-    if (rvar < 0)
-      error->all(FLERR,"Variable name for region sphere does not exist");
-    if (!input->variable->equalstyle(rvar))
-      error->all(FLERR,"Variable for region sphere is invalid style");
-  }
+  if (rstr) variable_check();
 }
 
 /* ----------------------------------------------------------------------
@@ -168,3 +164,16 @@ void RegSphere::shape_update()
   if (radius < 0.0)
     error->one(FLERR,"Variable evaluation in region gave bad value");
 }
+
+/* ----------------------------------------------------------------------
+   error check on existence of variable
+------------------------------------------------------------------------- */
+
+void RegSphere::variable_check()
+{
+  rvar = input->variable->find(rstr);
+  if (rvar < 0)
+    error->all(FLERR,"Variable name for region sphere does not exist");
+  if (!input->variable->equalstyle(rvar))
+    error->all(FLERR,"Variable for region sphere is invalid style");
+}