Panomifene (PAN) /E/-1,2,-diphenyl-1-[4-[2-(2-hydroxyethylamino)-ethoxy]-phenyl]-3, 3,3-trifluoropropene is a new original Hungarian compound and is a tamoxifen (TMX) analog. In the phase I/a study presented here the human tolerance, pharmacokinetics and endocrine effects of a single oral dose of panomifene were evaluated in healthy, post-menopausal, female volunteers. As to the dose escalation, pharmacokinetic studies were carried out at doses of 24, 48 and 96 mg in two volunteers, and 120 mg in one volunteer. To find a suitable dose or dose range, for further evaluation of the drug detailed pharmacokinetics were performed at a selected dose level (24 mg) in 10 volunteers. The pharmacokinetic study showed considerable interindividual variability of the parameters, and only a medium correlation between dose and AUC (r=0.876). At the selected dose level (24 mg p.o.) the peak concentration of the plasma was 67.7 +/- 17.4 ng/ml (Cmax(meas)), the time to peak was 3.6 +/- 1.8 h (t[max(meas)]). The mean of the terminal half-life was 70.0 +/- 23.1 h (t(1/2beta)). The area under the plasma concentration time curve (AUC) calculated by the kinetic equation (AUCcalc) was 4814 +/- 1172 and by the trapezoidal rule (AUCtrap) was 4612 +/- 1357 (ng/ml) h.