An attempt was made to elucidate the interaction between PCB toxicity and vitamin A. The effects of vitamin A addition or vitamin A deficiency in altering the toxicity of dietary PCB were examined. Rats fed a 0.1 PCB diet supplemented with 3,400 IU of vitamin A for 6 weeks showed better growth than those fed a 0.1% PCB diet only. However, rats given a vitamin A deficient diet with 0.1% PCB showed a significant growth retardation than those given a 0.1% PCB diet only. All rats which were fed a vitamin A deficient diet with PCB closed their eyes 50% or entirely in the last period of the experiment, but such sym ptom was not seen in the rats given a 0.1% PCB diet only or a vitamin A deficient diet. Vitamin A content in the liver decreased significantly with 0.1% PCB administration. It was found that a larger supply of dietary vitamin A than the level contained in the basal diet is required to prevent, to some extent, the growth retardation by PCB administration and to sustain the same level of vitamin A content in the liver of rats fed the same 0.1% PCB diet as that of basal diet group. It was concluded that animals fed PCB require more vitamin A than usual. This suggests the possibility that vitamin A may play a role in the dntoxication of PCB.