The reproductive endocrinological characteristics of beluga, killer whale, spotted seal and bottlenose dolphin were evaluated and used in conjunction with applied reproductive research to enhance captive breeding programs. Results from 8 y of biweekly serum progesterone determination in a female beluga indicated that sexual maturity occured at approximately age 13, two to seven estrous cycles, lasting 37 ± 3.9 days, per yr began in April-May every year. Rectal temperature was positively correlated with serum progesterone levels and negatively associated with behavioral estrus. In five cases of pregnancy of two female killer whale, positive relationship was found between serum progesterone concentration and temperature during the first period of 18 month-gestation. In the normal parturitions (n=4), rectal temperature decreased 0.8 C lower than average rectal temperature during pregnancy. Sexual maturity of female killer whales occurred at age nine. Yearly contraception in the mono-estrus captive spotted seals (n=10) using a single dose of the progestagen (proligestone^TM; 5 or 10 mg/kg s.c.) was achieved in 94% (33/35) of the attempts over 5 yr when the hormone was administered two months prior to the breeding season. Artificial insemination trials (n=4) were conducted in female bottlenose dolphin (n=3) using fresh and frozen-thawed semen. Estrus synchronization using regumate (27 days) resulted in ovulation occurring 19 to 24 days post withdrawal. Conception was confirmed in 75% of the attempts, with two females successfully delivering calves.