Chickens were adapted to their handler before the experiment. Adapted birds produced more antibody, had more blood protein, gained more weight, and were more resistant to Mycoplasma gallisepticum than unadapted birds. The antibody response to sheep red blood cells was not reduced for fasting for 48 hours in adapted birds but was in unadapted birds. Differences in antibody titers, blood protein, and weight gains between controls and birds fed 80 ppm of deoxycorticosterone could be demonstrated only with adapted birds.