Tamoxifen, a non-steroidal antiestrogen, is used in the palliative treatment of advanced breast cancer and as an adjuvant therapy after mastectomy. The bioequivalence of tamoxifen following single oral doses of Zemide 20 and a commercially available tablet formulation (reference formulation), each containing 30.4 mg tamoxifen dihydrogencitrate corresponding to 20 mg tamoxifen was investigated in 12 healthy male subjects. In a randomized, crossover study with a washout period of 13 weeks the volunteers received one pharmaceutical unit of both formulations after an overnight fast on an empty stomach. Plasma concentrations of tamoxifen were determined at predose and predetermined time points up to 20 days after administration using a validated HPLC method. The two tamoxifen formulations were proven to be bioequivalent for tamoxifen regarding rate and extent of absorption. The bioequivalence decision was based on Cmax, tmax and AUC0-t.