Serum vitamin A and retinol-binding protein (RBP) levels were determined in a group of 34 children between 1 and 4 years of age with failure to thrive and in 34 age- and sex-matched controls. Both groups of children were also assessed in respect of anthropometry and diet. Vitamin A levels in patients (0-32.2 micrograms/100 ml; median 16.9 micrograms/100 ml) did not differ significantly from controls (6.4-47.2 micrograms/100 ml; median 16.1 micrograms/100ml). Fourteen patients (42%) and 4 controls (12%) had vitamin A levels below 10 micrograms/100 ml. RBP levels in patients (0.45-3.50 mg/100 ml; median 2.17 mg/100 ml) also did not differ significantly from those in controls (1.21-3.66 mg/100 ml; median 2.06 mg/100 ml). No clinical features of vitamin A deficiency were detected. Weight and height for age, weight for height, mid-upper arm circumference and head circumference differed significantly between patients and controls (P < 0.0001 in each instance). Although within the recommendations for intake, patients had a significantly lower intake of the essential fatty acid C 18:2 (N = 6) (linoleic acid) and vitamin A. In view of the current proposed relationship between vitamin A status and infectious diseases, the prevalence of biochemical vitamin A deficiency in children in the Cape Town community studied may contribute to the morbidity and mortality associated with infectious diseases in the area to a greater degree than has been suspected.