The transvaginal bioavailability of 200 mg progesterone (CAS 57-83-0) from a vaginal capsule (Utrogest 200) compared to a vaginal gel containing 90 mg progesterone per dose was evaluated in 24 healthy young women using a randomised two-period cross-over design. Both treatments were supposed to release comparable amounts of progesterone. Blood samples were taken over a period of 96 h following single administration. Pharmacokinetic evaluation of both formulations was based on progesterone concentrations in serum measured by a validated RIA method. The relative bioavailability was determined as ratio of the AUC0-infinity and cmax together with the 90% confidence intervals. It could be demonstrated that one vaginal capsule containing 200 mg progesterone has a higher bioavailability than a dose of gel containing 90 mg progesterone. After administration of the capsule almost 50% more progesterone was bioavailable than after gel application. Both treatments did not vary with respect to the measured peak concentrations. However, tmax was clearly different. There were no relevant differences in safety profile between the two preparations investigated. Both were well tolerated.