SummaryUnderstanding of the physiology of luteinising hormone-releasing hormone (LHRH) has increased rapidly over the 12 years since the hormone was elucidated and synthesised (Schallyet al., 1972). It was initially hoped that the hormone would fulfil a role as an agent for both the stimulation and inhibition of gonadal function. These hopes were not fulfilled until the physiology of release and effect of LHRH was elucidated in greater detail (Knobil, 1980). The role of the hormone appears under normal conditions to be the permissive regulation of the gonadotrophins by pulsatile release every 90-180 minutes. LHRH and its analogues have an effect on the pituitary gland which is dependent on both dose and method of administration. Low doses of the drug given in a pulsatile fashion activate both gonadotrophic responsiveness and gonadotrophin reserve. Continuous infusions or high dose pulsatile infusion cause loss of pituitary sensitivity and loss of gonadotrophin secretion. Long-lasting LHRH analogues cause a similar effect to that found after high doses of the natural hormone.