Amprolium may be used as a coccidiostat in rearing hens and is a therapeutical agent used in laying hens. As a result of cross contamination, low amprolium levels may occur in feed. Feed containing a concentration of amprolium ranging from 5 to 250 mg/kg was therefore supplied to groups of laying hens. The amprolium residues in the yolks during and after treatment were subsequently determined. These levels varied from 1.75 mg/kg in the group fed 250 mg/kg to 0.2 mg/kg in the group fed 5 mg/kg. Amprolium levels in the whites of eggs were much lower than those in the yolks. The residues in yolks decreased below detectable levels (less than 0.005 mg/kg) within approximately ten days after treatment. Rearing hens in a tiered wire floor system were given amprolium in their feed until the first egg was laid. Amprolium residues in yolks were detected for well over a fortnight after the onset of laying. The amprolium residues determined in yolk did not exceed US tolerance levels of 8 mg/kg.