The study attempted to determine if heavy physical labour by mothers during pregnancy affected fetal growth when such mothers had calorie intakes which were below 70 per cent of WHO/FAO recommended standards. Full term infants of such mothers had a mean birth weight of 3060 +/- 355 (SD) g compared to 3270 +/- 368 SD g for the newborn of less physically active mothers on similar low calorie diets (P less than 0.01). The mothers who engaged in heavy labour had a mean pregnancy weight gain of 3.3 +/- 2.4 (SD) kg, independent of the birth weight of their offspring, compared with 5.9 +/- 3.3 kg for the less active mothers (P less than 0.001). The mothers' weight in early pregnancy had an insignificant influence on birth weights when mothers were on low calorie intakes.