A simple capillary zone electrophoresis (CZE) method is described for the simultaneous determination of cimetidine (CIM), famotidine (FAM), nizatidine (NIZ), and ranitidine (RAN). The analysis of these drugs was performed in a 100 mm phosphate buffer, pH 3.5. Several parameters were studied, including wavelength for detection, concentration and pH of phosphate buffer, and separation voltage. The quantitative ranges were 100-1000 muM for each analyte. The intra- and interday relative standard deviations (n = 5) were all less than 4%. The detection limits were found to be about 10 muM for CIM, 20 muM for RAN, 20 muM for NIZ, and 10 muM for FAM (S/N = 3, injection 1 s) at 214 nm. All recoveries were greater than 92%. Applications of the method to the assay of these drugs in tablets proved to be feasible.