Although passive stretching is widely used, the parameters of stretching necessary to achieve a lasting length have not been determined. This study investigated the lasting effects of one bout of two 15-second passive stretches on ankle dorsiflexion range of motion. Conducting this study was important because, while it focused on a sufficient minimum duration, it considered lengthening mechanisms thought to contribute to a lasting length. Nineteen healthy volunteers with symmetrical limitations of ankle dorsiflexion participated. Stretching was done in unilateral standing with the subject's heel suspended over the edge of a platform. Four 5-second active dorsiflexion contractions were used as a preconditioning intended to stabilize the effects of mechanisms providing temporary length gains and were found to be effective. Measurements of passive dorsiflexion range of motion were taken over 24 hours. This study found no statistically significant length gains using a single bout of two 15-second stretches. These data do not provide evidence of lasting lengthening at this duration. Further research to determine a minimum one-bout lasting length duration is encouraged.