The Florida manatee is a unique marine herbivore of the order Sirenia. This endangered species is found in coastal and estuarine waters of Florida throughout the year. Manatees become sexually mature at 3-5 years of age. Sexually active animals will form mating herds, lasting 2-4 weeks, consisting of a single female pursued by numerous males. Manatees do not have a well-defined breeding season, but rather a diffuse reproductive period with peaks of activity in the spring and lulls in the winter months. Monitoring both hormones and behavior allows us to more accurately identify reproductive phases and improve our understanding of Florida manatee reproductive biology, thus enhancing our population models, management decisions, and ability to recognize differences between healthy and unhealthy states. The overall goal of this study was to 1) characterize fluctuations in hormone concentrations (17β-estradiol, progestogens and cortisol) from fecal, urine and plasma samples, 2) collect vaginal smears to monitor changes in vaginal epithelium, and 3) collect behavioral data that might be correlated with estrous cycle patterns and potential stressors. The majority of samples were collected from captive animals. Of the captive animals two females were trained for husbandry behaviors to facilitate collection of feces, urine, blood and vaginal smears. Of the remaining captive and wild animals, only fecal samples were collected. Repeated sampling of all captive and one wild, tagged female was possible, but fecal samples from all other wild animals were collected on an opportunistic basis. Behaviors from all captive animals were monitored. Captive animal estradiol and progesterone values measured from weekly fecal samples collected over a one-year period indicated an estrous cycle length of approximately 28-42 days. Daily fecal samples collected from trained animals over a five-month period show a luteal phase of 18.5 days, STD 4.2, range 14-28 days. Seasonal fluctuations in hormone concentrations were observed with slight peaks during spring and/or fall. Preliminary data of cortisol concentrations indicate lower cortisol values for wild animals compared with captive animals. Some behaviors such as social contact did correlate with hormone fluctuations. Additional samples are currently being assayed, luteinizing hormone (LH) and follicle stimulating hormone (FSH) will also be measured in urine and plasma samples, plus gas chromatography/mass spectrometry (GC/MS) will be used in the near future to further quantitate and identify major metabolites in each of the sample types (urine, feces and blood).