Fourteen 15-kg hand-raised lambs were subjected to exposure to -5 deg C for three hours each day for 4 days. The greatest increase in heart rate occurred at the second hour of cold shock, when ambient temperatures were lowest. This increase became successively smaller each day. The greatest rectal temperature decreases occurred after 3 hr of cold shock, 1 hr after the minimum ambient temperature had been reached. This rectal temperature decrease became successively greater each day.