The purpose of this study was to investigate the direct action of one of the main constituents of cigarette smoke on corpus luteum function. Progesterone and estradiol production were measured in the presence and absence of nicotine as free base or bitartrate salt with or without luteinizing hormone (LH) stimulation using radioimmunoassay in an in vitro granulosa cell culture system. Human granulosa cells were obtained from 19 patients undergoing in vitro fertilization embryo transfer treatment for infertility at the University Women's Hospital, Tübinge, Germany. Nicotine free base augmented estradiol secretion and inhibited progesterone secretion by human granulosa cells in a dose-dependent manner. Nicotine bitartrate had little effect on steroid secretion. If granulosa cells were stimulated with LH, both nicotine preparations suppressed estradiol secretion, however, only nicotine bitartrate additionally inhibited progesterone secretion. The results suggest that cigarette smoking specifically affects the control mechanisms of intraovarian processes which are responsible for normal luteal function.