The level of locomotor activity, body temperature (T(B)), and feeding for adult (3-5-month old) and aged (22-24-month old) male BALB/c mice was determined and the sensitivity of the two age groups to the anorectic, febrile, and behavioral properties of interleukin-1beta (IL-1beta) in the brain was examined. Baseline locomotor activity and T(B) were markedly lower in aged mice than in adults and the circadian rhythm for both activity and T(B) were disrupted in the aged. Adult and aged mice consumed similar amounts of food during the daytime and nighttime, but aged mice made longer, less frequent visits to the feed cup. To determine if aging affects the responsiveness to central IL-1beta, adult and aged mice were injected intracerebroventricularly with PBS or IL-1beta. Compared to age-matched PBS controls, IL-1beta increased T(B) in both adult and aged mice. The peak deltaT(B) was greater in aged mice than in adults, but because of a lower baseline T(B) in aged mice, peak T(B) after IL-1beta was not different between groups. Locomotor activity of aged mice receiving PBS was about half that of PBS-injected adults and was not depressed further by IL-1beta. However, compared to age-matched PBS controls, centrally administered IL-1beta depressed food intake more in aged mice than in adults. These data indicate that even though feeding, locomotor activity, and T(B) are affected by aging, the central component of the inflammatory response mediated by IL-1beta is retained.