Total 24-hour urinary oestrogen has been used extensively and proven to be reliable in monitoring gonadotrophin therapy for induction of ovulation. However, the method is time consuming for the patient and incomplete collection, as expected, is not uncommon, hence interfering with the treatment result. Oestrone-3-glucuronide in first morning urine samples has been shown to correlate well with plasma oestradiol-17 beta levels during normal menstrual cycles. A comparative study was made to examine the correlation between the levels of 24-hour urinary oestrogen and first morning urinary oestrogen in patients on gonadotrophin therapy. Creatinine levels were also determined to exclude the factor of variable excretion of oestrogen. The correlation thus found is highly significant (p less than 0.001). Hence first morning urinary oestrogen to creatinine ratios may be used to replace 24-hour urinary oestrogen in biochemical monitoring of gonadotrophin therapy.