In this study, we examined the relationship between concentrations of maternal serum alpha-fetoprotein (MSAFP) and maternal serum human chorionic gonadotropin (MShCG) in the second trimester and the haemolysis, elevated liver enzymes, low platelet count (HELLP) syndrome. The concentrations of both serum markers, expressed in multiples of the median (MOM), in 16 women with the HELLP syndrome were compared with those in 10443 women without this syndrome who were screened for Down's syndrome and neural tube defects. All the women with a singleton pregnancy and a known pregnancy outcome were included in this study. At a cut-off level of 2.5 MOM, 37.5 per cent of the pregnancies with the HELLP syndrome had an elevated MShCG level, compared with 4.8 per cent in the whole population (P < 0.0001). 12.5 per cent of the women with the HELLP syndrome had an elevated MSAFP level, compared with 1.3 per cent in the whole population (P < 0.025). Women with a combined elevation of MSAFP and MShCG levels (0.3 per cent of the screened population) had a 47 time greater risk of developing the HELLP syndrome than the others (P < 0.01). The HELLP syndrome should be taken into account in the case of unexplained elevated levels of MShCG and MSAFP, especially in the rare event of combined elevation of both markers.