(not a well chosen 'subject' ...)

> UPDATE PTDEMOG
> SET SPECIMENID = :counter;

where ?????? <==========

>END
>
>but it updates all PTDEMOG.SPECIMEN_ID fields
>with the same SPECNO.SPECIMEN_NO value.

Without a WHERE clause you have specified that all rows are to be updated.

Regards,
Aage J.