This project was supported in part by a grant from The Foundation for Physical Therapy, 1111 North Fairfax Street, Alexandria, VA 22314 Foreshortened hamstring muscles have been associated with various clinical disorders. This study examined the effects of three weeks of daily static stretching of short hamstrings on passive straight leg raising (SLR), maximal hamstring length (MHL), and their maximal resistance to passive stretch (MRPS). Twenty-four healthy men (18-37 yrs) with SLR </= 70 degrees were assigned randomly to a stretching group (N = 12) or a control group (N = 12). All subjects were positioned on their left sides with the pelvis stabilized and the right thigh fixed at 90 degrees on a horizontal platform. The right knee was then passively extended until amplified EMG activity (>50 muV) from the hamstrings was observed. The knee angle represented MHL, and MRPS (torque in nm) was calculated. Subjects in the stretching group completed daily static stretching of the hamstrings for three weeks. After three weeks, SIR increased for the stretching group, but not for the control group (< 0.001). The knee angle for the stretching group was less than the control group (p < 0.001), and the MRPS for the stretching group exceeded the control group (p < 0.05). The results indicated that static stretching increased SLR with concomitant increases in the MHL and the MRPS. The results also support using SLR as a valid clinical test for measuring hamstring length changes resulting from therapeutic interventions. J Orthop Sports Phys Ther 1991;14(6):250-255.