You can do it by formula using data validation without the
need for VBA
data|validation| use the drop down to select Custom
in the formula box enter =if(g15<0,0)
then add a message that you want displayed

dave


-----Original Message-----
OK here's the scenario I need:

When User enters data in G15, I15 needs to prevent entry.
If User clears data in G15, I15 needs to allow entry.

I know this is easy but I'm still learning VBA.
.