The acute effect of stretching on the kinematics of the vertical jump was investigated in a sample of 20 young adults. Sagittal plane videography (60 Hz) was used to measure the kinematics of vertical jumps after 2 warm-up routines, control and stretching. Subjects were tested on 2 occasions with warm-up routine randomized. There were no significant changes in vertical velocity, knee angle, or the durations of the eccentric and concentric phases as a result of stretching despite good statistical power for the tests. Fifty-five percent of the subjects had lower vertical velocities (-7.5%) after stretching, while 45 percent of the subjects had no change (10%) or higher vertical (35%) velocities (2.4%) after stretching. Stretching prior to stretch-shortening cycle activities like the vertical jump results in small decreases in performance in some subjects, but the nonsignificant biomechanical changes suggest that neuromuscular inhibition may be the mechanism rather than changes in muscle stiffness.