A novel method for the determination of alkaline phosphatase (ALP) isoenzymes in individual fibroblast cells of mouse bone marrow was developed by combining capillary electrophoresis with an on-capillary enzyme-catalyzed reaction and electrochemical detection. In this method, a single an cell, followed by 5.0 x 10(-2) mol/L Na2B4O7-3.0 x 10-2 mol/L NaCl (pH 9.8) as cell lysis solution, was injected into the inlet of the separation capillary by electromigration. The cell was lysed by applying a voltage of 2 W The ALP isoenzymes in the cell were preseparated at 20 kV for 1 min, and then allowed to react for 30 min with disodium phenyl phosphate as enzyme substrate in the running buffer. ALP converted disodium phenyl phosphate into its product, phenol, at a relatively high reaction rate Without consumption, with resultant amplification of the signal on prolonged reaction time, producing an adequate amount of product for final detection. A mass detection limit as low as 3.5 x 10(-21) mol/L (corresponding to 1.5 nU) was achieved. Finally, the two zones of products generated by ALP isoenzymes were detected at the outlet of the capillary by using the end-capillary amperometric detection at a carbon fiber microdisk bundle electrode with a constant potential.