Postnatal weight gain during the first 8 weeks of life of 20 very low birthweight preterm infants (gestational age: 28.9 +/- 1.7 weeks, birthweight: 1098 +/- 199 g, mean +/- SD) was compared to the in utero weight gain of theoretical control fetuses. By the end of the study period preterm infants gained significantly less weight than their controls (155 +/- 15 vs 221 +/- 16%, p less than 0.001). During the first 6 weeks of life daily additional weight gain of the preterm infants was less than that of the controls, but after that time no significant difference was seen (7th-8th week: 12.0 +/- 3.6 vs 13.7 +/- 3.9 g/kg/day, study infants vs controls, ns). During the 7th-8th weeks of life positive correlation was found between calorie intake and weight gain (r = 0.33, F = 2.17, p less than 0.05). The changes in serum total protein and albumin levels, including an initial increase by the age of 2 weeks, were statistically not significant.