The purpose of this study was to examine the possible causes of poor reproductive performance in young bitches by examining behavioral-ovarian-endocrine correlates at the first pubertal proestrous-estrous interval. The results indicated that some, but not all bitches exhibited one or more atypical reproductive patterns at pubertal estrus and that these aberrant patterns appeared to be related to endogenous hormonal insufficiencies or irregularities. Although ovulation was detected in all dogs examined, atypical observations included lack of sexual receptivity and reduced or inconsistent patterns of circulating concentrations of estradiol, luteinizing hormone, or progesterone.