The equations for the coulometric efficiency eta and steady state current I-s (A) for the end-column amperometric detector in capillary zone electrophoresis have been investigated; they can be expressed as follows : eta = 1 - m(1) exp(-m(2)DA/Ub) and I-s = nFcU[1 - m(1) exp(- m(2)DA/UB)] where D (cm(2)s(-1)) is the diffusion coefficient of the species detected, A (cm(2)) is the area of the electrode, U(cm(3)s(-1)) is the mean volumetric velocity, b (cm) is the distance between the electrode and the capillary outlet, c(molcm(-3)) is the concentration of the species detected in solution, and n and F have their normal significance. m(1) and m(2) are constants which can be determined by experiment. The two equations have been verified experimentally.