Plasma levels of oestradiol and progesterone in 3 pumas during oestrus and artificially induced pregnancy and pseudopregnancy were determined by radioimmunoassay. During oestrus, basal levels of oestradiol (5-30 pg/ml) were interrupted by surges of 30-375 pg/ml at intervals of 17-25 days. Considerable variation occurred between and within animals. Periods of oestrus and follicular development were confirmed by laparoscopy and vaginal smear patterns. Absence of an increase in plasma progesterone following elevated levels of oestradiol and failure to observe corpora lutea in the ovary indicated that ovulation was probably not spontaneous. Plasma oestradiol values rose dramatically in response to PMSG but were low during pseudopregnancy until the return to oestrus. During pregnancy surges of oestradiol occurred at mid-term and immediately before parturition. Ovulation, confirmed by laparoscopy, occurred 24-48 h after hCG and progesterone levels (usually less than 2 ng/ml) then increased to reach 150-300 ng/ml on Days 24-28. In the pseudopregnant animals progesterone concentrations had returned to baseline by Days 45-50 but during pregnancy progesterone remained elevated, declining only gradually to basal values by Day 85. A minor peak of progesterone, coincident with the pre-partum oestradiol surge, occurred on Day 87, 1 week before parturition on Day 95.