Hi,
I recently created a base mesh in Blender and imported it in to Zbrush. I noticed that there were holes in the mesh, so I turned the button double on and that fixed the problem. I divided the mesh a couple of times but the holes started to reappear (more rounded). I would really appreciate any help with this. 
Thanks in advance
Regards Zubin
Tool > Geometry > Close Holes may help.
Hi Thanks for the reply.
I do not see that option to fill the hole. I am running ZBrush on Mac and it is 3.12.
That’s a ZBrush 3.5 feature. You should be using 3.2 though rather than 3.12. See the link in my signature.
It sounds like your model probably has overlapping points that aren’t welded. As the model is divided, the smoothing algorithm causes those points to start pulling apart, creating holes. When exporting from your other application make sure all points are welded. Or when importing into ZBrush increase the value of the Tool>Import>Weld slider. If welding is not an option, press Tool>Geometry>Crease before dividing the model. This will prevent those edges from pulling apart.