To investigate the efficacy of stretching with ice for increasing hamstring flexibility.Supine hamstring flexibility was measured before and after subjects accomplished a 20-minute hamstring stretching routine. Two groups of eight subjects accomplished the routine using one of two modalities. A control group (n = 8) accomplished the routine without a modality. The measurements were compared.Twenty-four male collegiate baseball players.Heat or ice applied to the hamstring.We found differences in the responses among subject groups. Supine hamstring flexibility after stretching with ice was greater than both stretching with heat and stretching alone. Scores after stretching with heat and stretching alone were not different.The results of our investigation suggest that the application of ice may provide enhanced short-term improvements in hamstring flexibility over heat or stretching alone. Further research is necessary to investigate the possible mechanisms for these improvements and to determine whether similar results can be obtained with other muscle groups.