This investigation examined the effects of a protease supplement on selected markers of muscle damage and delayed-onset muscle soreness (DOMS). The study used a double-blinded, placebo-controlled, crossover design. Twenty men (mean +/- SD age = 21.0 +/- 3.1 years) were randomly assigned to either a supplement group (SUPP) or a placebo group (PLAC). All subjects were tested for unilateral isometric forearm flexion strength, hanging joint angle, relaxed arm circumference, subjective pain rating, and plasma creatine kinase activity and myoglobin concentration. The testing occurred before (TIME1), immediately after (TIME2), and 24 (TIME3), 48 (TIME4), and 72 (TIME5) hours after a bout of eccentric exercise. During these tests, the subjects in the SUPP group ingested a protease supplement. The subjects in the PLAC group took microcrystalline cellulose. After testing at TIME5 and 2 weeks of rest, the subjects were crossed over into the opposite group and performed the same tests as during visits 1-5, but with the opposite limb. Overall, isometric forearm flexion strength was greater (7.6%) for the SUPP group than for the PLAC group, despite nearly identical (difference = 0.14 N.m, p = 0.940) mean strength values before (TIME1) the eccentric exercise protocol. There were no between-group differences for hanging joint angle, relaxed arm circumference, subjective pain ratings, and plasma creatine kinase activity and myoglobin concentration from TIME1 to TIME5. These findings provided initial evidence that the protease supplement may be useful for reducing strength loss immediately after eccentric exercise and for aiding in short-term strength recovery. The protease supplement had no effect, however, on the perception of pain associated with DOMS or the blood markers of muscle damage.