The purpose of this two-part study was to determine whether the amount of exercise-induced muscle soreness differs between subjects who perform concentric and eccentric isokinetic contractions of their quadriceps femoris muscles. In experiment 1, subjects were randomly assigned to either an eccentric or a concentric exercise group and both groups exercised at the same power level. In experiment 2, subjects were randomly assigned to either an eccentric or a concentric exercise group and both groups exercised with maximal effort. Muscle soreness ratings, obtained by using a visual analogue scale, were taken immediately before exercise and at 24 and 48 hours postexercise. Changes in muscle soreness ratings between exercise groups from preexercise to postexercise periods were compared in both experiments, using a one-way between-subjects analysis of variance. There was no difference in the change in muscle soreness from preexercise to post-exercise periods between groups exercising at equal power levels. Subjects who exercised using eccentric contractions with maximal effort demonstrated greater increases in muscle soreness than those who performed concentric contractions. The results suggest that exercise intensity, rather than contraction type, may be the dependent factor in producing exercise-induced muscle soreness.