Levels of retinol (vitamin A), carotenoids and triglycerides in the serum of 50 children with homozygous beta-thalassemia have been studied, as well as the ability of the small intestine to absorb a test meal containing retinol palmitate, triglyceride, d-xylose and glucose. On the other hand, 8 patients underwent a dark-adaptation test, and in 40 children with homozygous beta-thalassemia the levels of retinol-binding protein in the serum were estimated. The mean levels of retinol, carotenoids and triglycerides in the serum of the patients were: 23 +/- 4.1 micrograms/dl (controls: 36.3 +/- 4.9), 44 +/- 15.5 micrograms/dl (controls: 103 +/- 24), 117 +/- 20 (controls: 126 +/- 26), respectively. The absorption from the small intestine of retinol, triglycerides, glucose and d-xylose was normal. 6 out of 8 patients studied for visual function showed an abnormal dark-adaptation test, and these 6 children had low serum retinol levels. Finally, the mean serum levels of retinol-binding protein in the patients were 4.74 +/- 0.53 mg/dl (controls: 5.63 +/- 0.58). The low retinol levels were correlated with the low retinol-binding protein values which, in turn, could be due to the abnormal liver function of the patients.