Peo and Debra,
Thanks to both of you for your responses.

I'm just trying to understand this to forestall my embarrassment of such an
easy solution. I interpreted "Ignore blank" as "Do not fire the validation
in this field should you happen to be leaving this field while it is blank."
If one interprets it as such, this solution, while I see it works, shouldn't
make a difference.

Please explain how you two knew this.

Thanks again.

"Debra Dalgleish" wrote:

In the data validation dialog box, remove the check mark from Ignore Blank.

John S. Labarge wrote:
In cell A1, add following "custom" validation:
=not(isblank(b1))

As I see it, this should restrict leaving cell A1 unless cell B1 already has
a value.

I've also tried =b1<"" and some others. Should be simple but I can't get
it to work. Validation will not fire. For each equation I've tried, I've
cut and pasted the same equation into a field and it works fine.

--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html