A new analytical method is proposed for determination of hydralazine (HZ) in pharmaceuticals--measurement of the chemiluminescence (CL) emitted after reaction with phosphoric-acidified KMnO4. The novelty of this method is the recording of the whole CL-time profile. Such a recording is possible by use of a CL-detector operating in tandem which enables the reactants to be mixed in the measurement cell only and, therefore, the CL is reaction monitored from beginning. At the precise time the pump is stopped signal recording is triggered and so CL evolution is recorded completely. The optimum chemical conditions for the determination were 0.8 mol L(-1) formaldehyde, 0.3 mmol L(-1) KMnO4, 4.0 mol L(-1) H3PO4, and a total flow of 0.37 mL s(-1). Two calibration graphs were plotted, CL intensity and area under the profile curve against HZ concentration. Exhaustive statistical analysis provided very interesting results, for example, accordance with Clayton's theory, detection limit below 0.2 microg mL(-1), and linear calibration ranges from 0.2 to 5.0 microg mL(-1). This method was successfully applied to the determination of HZ in pharmaceuticals. Because they are usually formulated in association with diuretics and beta-blockers, the method was used for analysis of HZ in pharmaceuticals that contained either HZ only or HZ with other hypotensive substances. Obtained and nominal content were approximately the same and experimental Student t values indicated there were no significant differences between the values.