A novel aqueous progesterone formulation was developed. Study I: Three-way cross-over, open-label study in 24 post-menopausal women. Comparison of the pharmacokinetic profiles of a single 100 mg dose of test product administered by subcutaneous (s.c.) and intramuscular (i.m.) injection and an i.m. reference oily product. Study II: Three-way cross-over open-label study of 25, 50 and 100 mg s.c. single doses of the aqueous formulation in 12 post-menopausal women. Study III: Parallel-group, observer-blinded study in 25 fertile women administered multiple s.c. 25 and 50 mg doses of the aqueous formulation once daily for 11 days. Baseline-corrected pharmacokinetic parameters were evaluated. Aqueous formulation (100 mg) was promptly absorbed, achieving progesterone peak serum levels at an earlier time than the reference (1 h vs. 7 h; p < 0.0001). Test and reference were bioequivalent in the extent of exposure: confidence intervals for AUC(0-t) geometric means ratios were within the pre-specified 80-125% limits. Pharmacokinetics was linear over the range of doses studied. Steady state was reached within 4 days of multiple dose treatment. All treatments were well tolerated. Considering the advantages given by the possibility of self-medication, the s.c. aqueous formulation could offer a convenient alternative for patients on assisted reproductive technology treatments.