It is demonstrated that acetylcholine may be determined potentiometrically in capillary electrophoresis down to 6 x 10(-7) M with a miniature coated-wire ion selective electrode. The more established amperometric method is not possible for this compound. Similarly, 4-aminobutyric acid (GABA) is not accessible amperometrically; although potentiometric detection was possible, the sensitivity is not flood. Other neurotransmitters may be determined by either method, but in these cases amperometric determination is generally favorable. For serotonin the potentiometric detection limit was 4 x 10(-5) M, while for the amperometric method a detection limit of 10(-7) M was found.