BIOSIS COPYRIGHT: BIOL ABS. A trial was conducted to examine the effects of the interaction of an organic arsenical compound (roxarsone): 3-nitro-4-hydroxy-phenylarsonic acid and copper sulfate on the egg production, liver function, and the copper content of the liver, eggs and excreta of laying hens. The experiment was a 2ty 38-weeks-old layer hens were selected from a commercial flock, and placed into six dietary treatments, i.e. two levels of roxarsone (0, 50 mg kg-1) and three levels of supplementary copper (400, 500, 600 mg kg-1), with five layer hens in each cage. Feeding was undertaken for four weeks. The interaction between copper and roxarsone in the diet significantly influenced the feed intake, egg production, and copper content in the liver and excreta (P<0.05). Increasing the supplementation of copper from 400 to 600 mg kg-1 significantly depressed feed intake and egg production in both groups receiving diets with or without added roxarsone (P<0.05). Increasing the supplement o