Twenty-four hour urinary oestrogen results obtained in 20 amenorrhoeic patients undergoing human menopausal gonadotrophin (hMG) therapy have been analysed in detail in an attempt to improve their value in predicting multiple conception. Of 96 treatment cycles 88 were acceptably stimulated including 76 presumed ovulatory (midluteal serum progesterone concentration greater than or equal to 30 nmol/l). Conception occurred in 27 (26% of all, 33% of ovulatory cycles), of which 10 were multiple (37%). The chance of conception or multiple conception could not be related to luteal progesterone or preovulatory peak urinary oestrogen levels (at least within the clinically imposed limits of the oestrogen values). Discriminant analysis applied to all oestrogen results in individual cycles failed to predict conception, but in the conception cycles was 86% successful in predicting a single or multiple conception. Multiple conceptions were associated with an earlier but slower rise in oestrogen excretion during the last 5 days of hMG therapy, although the starting and final oestrogen levels were approximately the same. Unfortunately, the differences were small and as conception cycles were in the minority and could not be distinguished from non-conception cycles the oestrogen results could not be used reliably in practice to predict multiple pregnancy.