Thirty kittens were given a 30-min exposure to a moderately cool environment and drop in body temperature was measured. One group was tested every day from age 2 days to 21 days of age. A 2nd group was tested on Days 6-21 and a 3rd group tested only at 19 days of age. The 1st group (tested on Days 2-21) became homeothermic at an earlier age than did the other groups. The data are interpreted to indicate that early exposure to cool temperatures facilitates acquisition of temperature regulation in the cat, and that observed deficits in passive avoidance learning in young cats are not due to increased motor activity produced by a fall in body temperature.