Oral therapy with natural or synthetic estrogens, like ethinylestradiol, suffers from low, suboptimally defined bioavailability and excess hepatic estrogen actions. N,N-alkylated and non-alkylated sulfamates of ethinylestradiol, estradiol and estrone overcome these deficiencies. Ovariectomized Wistar rats (n = 6-7/group) were orally treated for 7 days, and killed on day 8, plasma was gained on days 0, 4, and 8. Systemic estrogenicity was quantified by assessment of uterine weight, vaginal cornification, and measurement of gonadotropins by homologous RIA. Estrogenicity in the liver was analysed. Angiotensinogen was estimated by RIA of angiotensin-1 after incubation of EDTA-plasma with porcine renin. Total and high-density cholesterol were measured by enzymatic methods. Preliminary biotransformation studies were performed after oral administration of 10 micrograms, 5 microCi [2,4,6,7-3H]estradiol sulfamate. Ethinylestradiol led to distinct elevation of angiotensin-1 and dramatic depression of cholesterol fractions, reflecting hepatic estrogen effects, already at doses with marginal systemic effects. Estradiol and estrone had systemic and hepatic estrogenic activity at much higher doses only. Estrogen sulfamates had systemic estrogen activity 10-90-fold above that of their parent estrogen. Non-alkylated sulfamates of given estrogens were more active than N-alkylated ones. Elevation of systemic estrogen activity was always combined with a dramatic reduction of hepatic estrogenicity. Estradiol sulfamate had a 90-fold elevated systemic estrogen activity vs estradiol, but lacked hepatic activity including the 30-fold dose inducing vaginal response. Three hours after administration no unchanged estradiol sulfamate was detectable in plasma. Rather peaks, probably representing estradiol and estrone, were found. Estrogen sulfamates are considered prodrugs of their parent estrogen, which do not interact with any liver function during the first-pass. They represent a new strategy of oral hormone administration. Their main potential seems to be the systemic generation of natural estrogens when used in oral contraceptives.