Circulating levels of luteinizing hormone (LH) are essential for the production of steroid hormones that regulate the timing of ovulation and target tissue responses, as well as maintenance of the corpus luteum and therefore early pregnancy. Clinical and basic science observations show that elevated levels of serum LH during the follicular phase of the menstrual cycle are not only unnecessary for follicular maturation but are deleterious to normal reproductive processes. These elevations may occur as a result of administration of exogenous LH or through an endogenous pathological process (i.e. polycystic ovarian disease, PCOD). Resting levels of LH, synergizing with locally produced IGFs, inhibin and perhaps other growth factors, are adequate for normal follicular growth and steroidogenesis. Elevations in serum LH above these resting levels may result in increased androgen production that diminishes follicular function and reduces early embryo viability. Elevated LH levels during the preovulatory period may also negatively influence post-ovulatory events such as conception and implantation. With these facts in mind, the best results for ovulation induction would be expected with purified follicle-stimulating hormone (FSH) administration to women following gonadotrophin releasing hormone (GnRH) down-regulation. It is hoped that this review provides the reader with an analysis of the complex series of events that regulate normal follicular maturation. The reevaluation of the two cell-two gonadotrophin theory suggests that during the preovulatory period, resting levels of LH are adequate for normal follicular maturation. Indeed, overstimulation of the ovary with excessive amounts of LH may diminish the ability of that target organ to produce fertile ova.(ABSTRACT TRUNCATED AT 250 WORDS)