Measles and protein energy malnutrition (PEM) in children have been associated with low serum retinol levels. Vitamin A supplementation has reduced mortality and morbidity significantly. The purpose of this study was to determine the effect of vitamin A supplementation on plasma retinol levels in children with these conditions.Black, African children, admitted to Ga-Rankuwa Hospital with measles or PEM, were randomly allocated to either a study or a control group. The study group received, in addition to routine treatment, 150 000 units of vitamin A palmitate IM on day 1 followed by 15 000 units orally for 7 days. The patients in the control group received routine appropriate treatment, which may have included 3000 units vitamin A per day. Retinol plasma concentrations of all patients were measured on days 1, 2, and 8.The mean baseline plasma retinol levels (day 1) of both the measles and PEM patients were lower than 11 μg/dl. There was a statistically significant increase in plasma levels in the study and control groups for both conditions by day 8 with the mean plasma retinol levels > 30 μg/dl. There was no statistically significant difference between study and control groups.This study has shown that there is a high incidence of baseline hyporetinaemia in these patients. The mean retinol plasma levels return to within normal limits after 8 days of either routine treatment or vitamin A supplementation.