A total of 418 pregnant women at 16-24 wk of gestation, from six subcentres of a rural block of Varanasi district were selected. Pregnant women (137 of 215) from 3 subcentres received the supplementation of 60 mg elemental iron as ferrous sulphate combined with 500 micrograms folic acid, daily for 100 days (study group) and 123 (of 203) pregnant women from the other 3 subcentres without supplementation (control group) could be evaluated for their pregnancy outcome. The haemoglobin and serum ferritin levels increased significantly in the study group. In the latter, the mean birth weight was 2.88 +/- 0.41 kg with low birth weight incidence of 20.4 per cent as compared to the control figures of 2.59 +/- 0.34 kg and 37.9 per cent respectively. The incidence of low birth weight was further reduced to 12.1 per cent if the supplementation could be started by 16-19 wk of gestation.