In Excel 2003

I've searched through the archives, but couldn't find a solution to my
particular problem.

In column B, I have filled from row 2 to row 1250 with:

=IF(blah blah,"",blah blah)

To find the last row in the column that isn't blank, I tried:

lr = Cells(Rows.Count, "B").End(xlUp).Row

which returns the value of 1250.

What I need is the last row in column B where the IF condition is FALSE, and
there is text in that cell.

TIA
David