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Ovulation induction is the most common medical intervention for the treatment of infertility. Clomifene is generally the first treatment choice for patients with amenorrhoea, unless there is profound hypothalamic deficiency. When clomifene fails to induce ovulation, menotropins (human menopausal gonadotrophin) or gonadotrophin-releasing hormone (GnRH) are effective, most notably in WHO group 1. In this condition associated with low estrogen and gonadotrophin levels, the aggregate of reported pregnancy rates is 25% per cycle. In hyperprolactinaemic anovulation bromocriptine reduces prolactin levels and thereby restores normal cyclicity. In all of the above conditions, the pharmacological agent addresses a specific defect in an explicit manner. WHO group 2 ovulatory disorders arise from hyperandrogenicity and other conditions that respond less predictably to gonadotrophin therapy. In women with WHO group 2 disorders, the aggregate of reported pregnancy rates is 8%. Ovulation induction is also used in ovulatory infertile women to generate multiple follicles and increase the likelihood of fertilisation. The aggregate of pregnancy rates in clomifene trials was 7% per cycle, and 6% in gonadotrophin trials. Gonadotrophin therapy is more effective, however, in association with assisted reproduction techniques. The contrasting treatment success in discrete disorders (25% per cycle) and heterogeneous disorders such as WHO group 2 and persistent infertility (6 to 8% per cycle) underlines the need for research to discover specific causal mechanisms and identify explicit new pharmacological interventions.