The effects of oxytetracycline (OXT) at doses of 0.291, 0.461, 0.922, 1.383 and 1.844 g/l in drinking water on the egg quality and on the fat content and fatty acid composition of egg yolk were studied. OXT had no effect on egg weight, yolk weight or shell thickness. Increasing availability of OXT in water reduced cholesterol and triglyceride in the egg yolk while it had no effect on the phospholipid content. OXT at higher doses favoured unsaturated and polyunsaturated fatty acids relative to saturated fatty acids in the yolk.