Human alpha-fetoprotein (AFP) was isolated from human abortive tissue by biospecific chromatography on immobilized estrogens. The most effective sorbents were: estrone-0-3-hemisuccinyl-hexamethylenediamine-Sepharose CL 4B and diethylstilbestrol-diasoanisole-sulfonyl-oxyethyl-Sepharose CL 4B. As elution solution the most optimum was 10% buffered aqueous butanol. Taking into consideration the data obtained, one can conclude that AFP in human biological fluids is bound to immobilized estrogens. Butanol extraction deestrogenizes AFP, and as a result human AFP acquires affinity to immobilized estrogens. During rechromatography on immobilized diethylstilbestrol, it was possible to obtain AFP preparations of about 95% purity. The present results provide the opportunity to work out new methodological approaches to human AFP isolation using biospecific chromatography on immobilized estrogens.