The sorbitol pathway was investigated in vitro on slices of umbilical cord tissue from normal full-term pregnancies. Glucose, sorbitol and fructose were shown to be present in this tissue at fairly constant levels. When added to the medium, these three substrates can be actively taken up by these preparations (in decreasing order: glucose > fructose > sorbitol). Incubation noticeably increases the sorbitol content of the tissue, especially when glucose is present in the medium, thus showing the presence of aldose reductase. Concentrated by ammonium sulphate fractionation, the proteins of this tissue showed a NAD+-linked sorbitol dehydrogenase activity, able to transform sorbitol into a ketose which, as shown by TLC, is probably fructose. Therefore, the complete polyol pathway is probably effective in this fetal vascular tissue.