"Dave F." wrote in message
...

CboElevation.Enabled = IsEmpty(ElevCptn)

IsEmpty() isn't for strings, it's for Variants that haven't been assigned a
value. IsMissing(), as Peter suggested, is only for Variants. Optional
parameters typed as anything besides a Variant that aren't given a default
value in the procedure declaration get the default for the data type, so
numbers get 0 and strings get empty strings. Therefore you should simply be
able to test ElevCptn against "". Did you ever try that?

Ron's Len() suggestion is also valid.