The aim of this study was to investigate the systemic bioavailability and plasma profiles of 17β-estradiol (E 2) after the application of three matrix patches for the transdermal delivery of E 2: Menorest™, Tradelia™, and Estraderm MX™ claiming to deliver a dosage of 50 μg E 2/day. All three patches were each worn randomly by 21 postmenopausal women volunteers over a 4-day period (i.e. 96 h). Each of the three treatment periods were separated by an at least 7 day wash out period according to a randomized, 3-way crossover design. Blood samples were taken from the antecubital vein before and 3, 6, 9, 12, 24, 28, 33, 48, 57, 72, 81, and 96 h after application. E 2 plasma values were determined by a specific direct radioimmunoassay method. The following pharmacokinetic parameters were evaluated: AUC 0–96h, C max, T max, C min, C average. The time to reach the maximal E 2 value of 32 h was the only pharmacokinetic parameter which was identical for all three patches. Menorest™ produced the highest E 2 bioavailability judged by the AUC 0→96h=3967.8±1651.8 pg/ml, C average=41.3±21.3 pg/ml, C min=36.8±8.6 pg/ml. Tradelia™ showed statistically not significantly smaller C average=38.9±17.0 pg/ml, AUC 0→96h=3737.9±1637.6 pg/ml·per h, and C min=33.8±26.7 than Menorest™. Estraderm MX™ showed lowest E 2 plasma profiles C max=38.9±25.1 pg/ml, C average=33.2±17.1 pg/ml, AUC 0→96h=3192.1±1646.0 pg/ml per·h. Menorest™ showed the smallest fluctuation over the entire test period, similar to Estraderm MX™, while Tradelia™ showed the highest E 2-fluctuation ( P<0.01): Tradelia™ exhibited the highest C max=48.0±20.3 pg/ml. When E 2 baseline levels, prior to patch application are subtracted individually from the produced E 2 plasma level, Estraderm MX™ is not bioequivalent to Menorest™ ( P<0.05). A circadian curve pattern of the E 2 plasma level was observed for all patches: in the evening higher E 2 plasma level were always detected compared with the morning, however, less pronounced with Estraderm MX™. Individual comparison of AUC 0→96h of each patch exhibited a large interindividual variability of 2000–8000 pg/ml per h for all three patches but relatively small individual variability: women with high E 2 bioavailability (high responders) maintained high bioavailability in all applied patches, women identified as low and medium responders remained the same regardless of the applied patch. Menorest™ produced in 2/3 of all postmenopausal women with the highest E 2 bioavailability (AUC 0→96h), Tradelia™ was found in less than 1/3 (28.6%), and Estraderm™ MX in only one postmenopausal woman. Menorest™only produced the highest reduction in postmenopausal symptoms together with Tradelia™. Estraderm MX™ produced a smaller reduction in postmenopausal symptoms compared to Menorest™ and Tradelia™. The observed side-effects were approximately equal in all three patches, with a maximum value after 72 h. It can be concluded that the three patches for the transdermal delivery of E 2 claiming to deliver 50 μg E 2/day differed from each other in their pharmacokinetic performance, although statistically not significant: Menorest™ exhibited the highest C average, AUC and C min, and the lowest fluctuation, followed by Tradelia™ and Estraderm MX™.