Vitamin A (retinol) status and the effect of a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 10 micrograms X kg-1, on vitamin A in the liver and serum, and on the hepatic UDP-glucuronosyltransferase (UDPGT) (EC 2.4.1.17) activity, were studied in heterozygous (GW) and homozygous (GG) Gunn rats. 1) Data from vitamin A analyses demonstrate that the amount of vitamin A stored in the liver of untreated Gunn rats is of the same magnitude as that of Sprague-Dawley rats. 2) The retinol content in the liver of both GG and GW rats was reduced to about 50% by TCDD-treatment. 3) Retinol levels in serum were found to be variable and no significant effect due to TCDD could be observed. 4) No correlation between the TCDD-induced reduction of vitamin A and the induction of UDPGT activity by TCDD could be demonstrated in this study. The vitamin A reduction caused by TCDD was considerably less in the Gunn rat than in the Sprague-Dawley rat, and the results indicate that the Gunn rat is more resistant to TCDD than other strains of rat. TCDD-induced reduction of liver vitamin A seems to some extent to correlate with TCDD-toxicity in different strains of rat. The specific properties of the Gunn rat and its relatively high resistance to TCDD make it a valuable tool in studies about the mechanism of TCDD-toxicity.