Twenty subjects performed for 11 min on a bicycle ergometer 30 sec following 5 min of prior exercise (PE) at each of four different intensities. PE was adjusted to maintain a heart rate of 110, 140, and 170 beats/min. The 4th treatment was no PE. Heart rate was an estimate of the mobilization of the cardiorespiratory system during exercise. The criterion task (CT) included cycling for 10 min against 3 kg resistance at 68 rpm followed by 1 min of an all-out work bout where subjects tried to complete as many rpm's as possible against 3 kg. The 11th minute was used to assure the complete exhaustion of energy reserves following the paced part of the task. Overall performance following PE-170 was significantly worse than that following no PE, PE-110, and PE-140, which was probably due to a build up of anaerobic metabolites such as lactate during the PE. Total work appeared to be greatest following PE-110, which showed a slight tendency toward better performance especially after the 6th minute. However, no clear cut evidence was produced to support the hypothesis that light to moderate PE would sufficiently improve performance by mobilizing the cardiorespiratory system, thereby reducing the initial oxygen deficit in the CT and thus allowing more work to be performed.