Using EXECUTE in plpgsql

Hi
I have just experimenting with plpgsql and cannot find out how to return
a single field from a query
that I know will only every return one field.  I currently use the
example below:

    qrystr1 := ''SELECT count(*) from my_table";
    FOR next_table IN EXECUTE qrystr1 LOOP
        next_table_count := next_table.count;
    END LOOP;

which seems like a very inadequate way to retrieve one value....?

Tips are very much aprieciated, thanks
Jonathon