The purpose of this experiment was to determine whether age differences in amounts of wheel running of starved rats were due to the frequency of bursts of running, to the average duration of bursts, to speed, or to any combination of these parameters. The experiment was carried out according to a 3 by 2 by 2 mixed model design. The independent variables were age (67, 293, and 746 days old at the start of starvation), food deprivation (total starvation vs ad lib), and occasion of measurement (initial vs maximum activity). The dependent variables were number of wheel revolutions, number of bursts of activity, number of seconds of running per burst, and revolutions per secono. The results indicated that acutely starved rats run more often, for longer periods, and at higher speeds than do sated rats, and that with increased age rats run less often, for a shorter time, and at slower speeds.The purpose of this experiment was to determine whether age-dependent decrements in the amounts of daily wheel running of starved rats were due to differences in the frequency of bursts of running, to differences in the average duration of running, to differences in the speed of running, or to differences in any combination of these parameters. With increasing weight loss, the amount of wheel running of young starved rats increases to a maximum and then decreases shortly before death (Campbell, 1964). This pattern of running changes only quantitatively with increasing age. A previous experiment (Jakubczak, 1967) indicated that, independent of drive level, amounts of wheel running of starved rats decrease with increasing age. In that investigation, the cumulative total of wheel running of starved rats decrease with increasing age. In that investigation, the cumulative total of wheel revolutions during 24 h was used as the dependent variable. However, rats do not run continually during the 24·h period, but distribute their running in a number of episodes or bursts of running (Slonaker, 1912). More recently, Premack and Schaeffer (1963) found that during a 1-h sample of running, starvation increases the cumulative amount of wheel running of rats by increasing both the frequency and average duration of bursts of running, but has little effect on speed of running. Consequently, the age differences in the amounts of wheel running of starved rats (Jakubczak,