PIP: A study to determine the pharmacokinetics of single doses of ethynylestradiol (EE) of 35-100 ug administered to a total of 98 women in the United States, Thailand, Nigeria, Sri Lanka, and Singapore. After EE ingestion, plasma samples were collected at various intervals with 65% of U.S. patients exhibiting peak plasma EE levels between 60-90 minutes, and 2/3 showed detectable EE levels at 24 hours using 50-80 ug doses. To assess within-subject variation and range of variation between individuals, subjects in Palo Alto using 35 ug doses were tested twice showing a variation within subjects of 51.8% and between subjects was 119%. In Tucson, subjects using 100 ug EE doses showed a within-subject variation of 13.5% and between subjects was 37%. Absorption phase half-life ranged from 14-22 minutes, distribution phase varied from 1-3 hours, and the elimination half life ranged from 6-14 hours. Nigeria indicated the lowest plasma EE levels while Thailand had the highest levels even when body surface differences were accounted for. Dietary differences may cause differences in drug absorption; in addition, differences in relative muscle/fat ratios could effect storage and metabolism.