Twenty consecutive infertile women (mean age +/- SD, 36.9 +/- 5.4 years) undergoing ovarian stimulation with recombinant follicle stimulating hormone (rFSH) were recruited. Serial measurements of plasma total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), apolipoprotein A1 (ApoA1), apolipoprotein B (Apo-B), lipoprotein(a) (Lp(a)), oestradiol and progesterone were performed on day 3 before starting ovarian stimulation, on the day of human chorionic gonadotrophin (HCG) administration and on day 15 after HCG administration, respectively. The relationship between lipid and apolipoprotein concentrations and serum oestradiol and progesterone concentrations was sought. All women completed the ovarian stimulation protocol successfully. Plasma concentrations of HDL-C and Apo-A1 were significantly raised on the day of HCG administration and then returned to baseline values within 2 weeks. LDL-C, TG, Apo-B and Lp(a) were significantly increased on day 15 after HCG administration. Lp(a) variation between the first sample and the third sample correlated positively with serum progesterone concentrations (r = 0.472, P < 0.04). No other significant correlations were found between lipid and apolipoprotein variations and either oestradiol or progesterone concentrations. It was concluded that an increase of plasma lipid and apolipoprotein concentrations deserves particular consideration and all women undergoing ovarian stimulation should be monitored for long-term atherogenic and thrombogenic risks.