Study Design: Prospective, researcher-blinded, repeated-measures, randomized complete block design. Objectives: To compare the effects of a single treatment of Pneumatherm, moist heat pack, and a control treatment on hamstring muscle length. Background: Traditionally, heating modalities have been used to facilitate increases in tissue length. The Pneumatherm has been developed over the past 20 years for use in the clinical treatment of a variety of musculoskeletal pathologies. However, there is no published evidence supporting the use of Pneumatherm for improving muscle length. Subjects: Participants consisted of 30 healthy, college-age males taken from a convenience sampling from the University of Indianapolis student population. Methods and Measures: Participants received a 3-treatment sequence on consecutive days. Treatments involved applying the determined modality to the posterior thigh using standard treatment protocols. A hand-held dynamometer was used to establish a consistent passive measurement force to measure hamstring muscle length. Results: A mixed-model analysis of variance with pretest-posttest (3 pretest and 3 posttest measures) and treatment sequence of the modalities (6 sequences of Pneumatherm, moist heat, and control) was completed. The only significant effect was for pretest-posttest measures. Post hoc comparisons revealed that the Pneumatherm posttest value was significantly different from all other measures. There were no differences found between pretest scores and the moist heat and control posttest scores. Conclusions: Our results demonstrate that the Pneumatherm modality is an effective agent for increasing hamstring muscle length following a single 20-minute treatment. In this study, a significant gain in hamstring muscle length was not found following a 1-time treatment with moist heat. The Pneumatherm may be a good option when heat is used to assist in gaining flexibility of the hamstring musculature.