1. Vitamin D deficiency was induced in anicteric Wistar rats, Wistar rats before common bile-duct ligation was performed and Gunn rats with unconjugated hyperbilirubinaemia.
2. The effect of ultraviolet radiation on plasma concentrations of 25-hydroxy-vitamin D was studied in a group of control anicteric Wistar rats (n = 11), Wistar rats 8 days after common bile-duct ligation (n = 7) with conjugated hyperbilirubinaemia and in Gunn rats (n = 11).
3. The plasma 25-hydroxy-vitamin D response to ultraviolet radiation was similar in the three groups.
4. It is suggested that neither conjugated nor unconjugated hyperbilirubinaemia prevent cutaneous vitamin D3 synthesis or 25-hydroxylation in the rat.