Basic Userform Controlsource question

[Kevin]

I've built a very basic userform, which works fine when I
hardcode cell adresses (i.e. 'patient data'!B4) for a
contol. I can't find docs on how to format the controlbox
to display the cell dynamically (i.e. sheets("patient
data").cells(rownum,2)).

I can't find the syntax/format to do this in the
Properties tool, ControlSource.

thanks

Kevin