Abstract: An extraction and assay procedure to measure fecal estradiol-17-beta and progestin concentrations in several cat species was developed and validated for use for noninvasive monitoring of ovarian function. Fecal samples were collected over a range of 3-20 months from female tigers (three), lions (three), snow leopards (three), cheetahs (two), caracals (two), and domestic cats (five). Samples were extracted with 90% methanol, lipids removed with petroleum ether, and the estradiol and progestins in the methanol measured by radioimmunoassay (RIA). High Performance Liquid Chromatography (HPLC) fractionation and subsequent RIA of the fractions indicated that the estradiol-17-beta antiserum cross-reacted primarily with estradiol-17-beta in the feces of lions and tigers and was assumed to be specific for estradiol-17-beta in the feces of other species as well. However, there were several immunoreactive compounds, presumably progesterone metabolites, excreted in the feces which varied both quantitatively and qualitatively among species. The behavior of tigers, lions, cheetahs, and caracals was visually monitored during the collection period and frequency of sexual behaviors was positively correlated with increases in fecal estradiol in all species observed. The mean fecal estradiol-17-beta peaks were as follows: tigers, 128.0 +- 13.1; lions, 186.0 +- 14.8; snow leopards, 136.7 +- 15.9; cheetahs, 140.9 +- 9.0; caracals, 24.5 +- 4.0; and domestic cats 158.9 +- 19.3 ng/gm. Fecal progestin concentrations rose significantly (P lt 0,001) only after breeding or during pregnancy and were as follows: tigers, 5.6 +- 0.6; lions, 1.9 +- 0.1; cheetahs, 8.4 +- 1.1; and caracals, 2.4 +- 0.4 mu-g/gm. Fecal progestins were elevated for one-half to two-thirds of the gestation length during presumed pseudopregnancy but remained elevated throughout successful pregnancies. These results suggest that ovarian function can be monitored noninvasively in the family Felidae by the measurement of fecal estradiol-17-beta and progestin concentrations.