Cryotherapy is a widely accepted component of treatment for acute injuries. It has recently re-entered the later stages of rehabilitation as a contributing modality. Cryotherapy's depressive effects on the body's physiological systems have generated concern among many health care practitioners about its effect on motor activity. This study examined the effects of an ice immersion on three functional performance tests: the shuttle run, the 6-m hop test, and the single-leg vertical jump. Twenty volunteers from Division III soccer and football teams who had not sustained an injury to the lower extremity within the past 6 months were randomly assigned to either an experimental or control group. Subjects in the experimental group performed three trials of each functional performance test before and after the application of a 20-minute ice immersion (13 degrees C) to the lower leg. Subjects in the comparison group followed the same procedure except that a 20-minute resting period replaced the cold treatment. A mixed design analysis of variance was used to analyze the data. Vertical jump scores decreased in the experimental group (41.4 +/- 6.8 cm to 39.3 +/- 6.1 cm) but not in the control group (45.2 +/- 5.5 cm to 45.7 +/- 5.9 cm) as a result of the treatment. Shuttle run times decreased in the experimental group (6.5 +/- 0.3 seconds to 6.7 +/- 0.4 seconds) but not in the control group (6.8 +/- 0.4 seconds to 6.8 +/- 0.4 seconds). Six-meter hop test values were not affected. We suggest that clinicians should carefully consider the immediate effects, potentially, of cold on motor activity.