The permeability of the blood aqueous and blood retinal barrier, the lens transmission, and the lens autofluorescence were measured by fluorophotometry in 7 diabetic youngsters treated by conventional therapy (mean age, 10.9 +/- 4.4 years), 9 diabetic youngsters treated by continuous s.c. insulin infusion (mean age, 12.3 +/- 5.0 years), and 13 healthy controls (mean age, 12.4 +/- 5.1 years). The mean permeability value for the blood retinal barrier of the diabetic juveniles did not differ significantly from that of the controls (P greater than 0.4), and no correlation with metabolic control (HbAlc) or duration of diabetes was found (P greater than 0.1). No differences in lens transmission larger than 4% were found. The mean value of lens autofluorescence corrected for normal age-dependency was found to correlate with the metabolic control: an increase of mean HbAlc by 1% resulted in an extra increase of autofluorescence by 11% (P = 0.002). This result suggests that good metabolic control can suppress excess lens autofluorescence, a precursor of cataract.