Chlortetracycline was fed continuously to laying hens at levels of 0, 50, 100, 150, and 200 g/ton for a period of 4 months. Eggs from hens on the hasal ration showed a miniscule rate of positives, 2.1%; eggs from hens fed 50, 100, and 150 g/ton showed a positive presumptive rate of 58.3, 11.8, and 3.5% and a measurable residue rate of 11.1, 83.8, and 94.9%; and eggs from hens fed 200 g/ton had a 100% measurable rate. Preparation of eggs by several cooking procedures indicated a 30–50% retention of potency.