The bioavailability of a single dose of intranasal nafarelin was evaluated in 15 healthy female volunteers. Each subject received a 400 micrograms intranasal and a 25 micrograms intravenous dose of nafarelin separated by at least 7 days. Blood samples were obtained frequently after each dose for determination of nafarelin plasma levels. After intravenous administration, time to maximum concentration (Tmax) was 2 minutes, and maximum serum concentration (Cmax) was 8.2 +/- 2.09 (SD) ng/ml. For intranasal nafarelin, mean Tmax was 18.4 +/- 7.9 minutes (range, 5 to 40 minutes), and Cmax was 2.04 +/- 1.29 ng/ml (range, 0.49 to 5.7 ng/ml). Systemic bioavailability of nafarelin ranged from 1.15% to 5.62% and averaged 2.82% +/- 1.23%. Nafarelin's bioavailability is adequate to achieve the desired therapeutic effect because of its inherent high biologic potency and its pharmacokinetic properties. Nafarelin is readily absorbed by the nasal mucosa, and therapeutic blood levels are rapidly achieved and maintained for a prolonged period of time.