Many pitching injuries occur during deceleration of the upper extremity when the muscles of the shoulder and arm are acting eccentrically. Published information re garding eccentric muscular strength in baseball pitchers is nonexistent. The purpose of this study was to assess bilateral isokinetic eccentric and concentric muscular strength of the shoulder's external and internal rotator muscles and the elbow's flexor and extensor muscles in a group of collegiate baseball pitchers (N = 25). Iso kinetic strength was assessed at 1.6, 3.7, and 5.2 rad/ sec. Our findings indicate that the internal rotator muscles were always stronger than the external rotator muscles and that the concentric and eccentric external- to-internal strength ratios ranged from 62% to 81 %. The eccentric strength of the shoulder rotator muscles av eraged 114% that of concentric strength. The concen tric and eccentric elbow extension-to-flexion strength ratios ranged from 71 % to 110%; eccentric strength av eraged 33% higher than concentric strength. No differ ences were noted between dominant and nondominant limbs for any of the strength measures or ratios. Clini cally, the findings of this study can serve as a reference during the evaluation, rehabilitation, and conditioning of throwing athletes.