A clinical pharmacokinetic bioequivalence study with two retard filmtablet preparations, both containing 20 mg of nifedipine (CAS 219829-25-4) was carried out. The investigated test preparation was Cordaflex 20 mg retard filmtablet. The pharmacokinetic parameters were determined after single and repeated administration in 15 and 16 healthy male volunteers, respectively, in open, randomised studies of cross-over design. Plasma levels of nifedipine were determined by HPLC with electrochemical detection using a robotic sample preparation technique. Statistical comparison of the pharmacokinetic parameters (AUC0-infinity, AUCss, tau tmax, Cmax, Css,min, Css,av, MRT, etc.) calculated from plasma concentration-time curves by ANOVAlog, confidence interval, Schuirman's, Westlake's, Anderson's and Wilcoxon's tests, furthermore the comparison of the clinical results did not show any significant difference between the two preparations. It is concluded that the two preparations are bioequivalent after repeated administration.