The purpose of this study was to compare the analgesic effect of pulsating ultrasound treatment and placebo on delayed onset of muscle soreness produced by an eccentric exercise bout. In addition, the effect of pulsed ultrasound on muscular performance following an eccentric exercise bout was studied. Eighteen untrained subjects were randomly assigned to: 1) ultrasound (A) [N = 6] over the areas of concentrated muscle soreness, i.e. proximal vastus lateralis and distal vastus medialis; 2) placebo ultrasound (B) [N = 6]; and 3) no therapeutic intervention (C) [N = 6]. Baseline data were recorded for maximum isometric knee extension contraction (MVC), maximum knee extension torque (MT), knee extension work (W), and soreness perception (SP). All values were subsequently reassessed 24 and 48 hours after intense muscular activity. Immediately following the 24 hour reassessment the A group received ultrasound treatment, the B group received placebo ultrasound, while the C group received no treatment. Percent deviation from baseline of SP, MVC, MT and W were significantly less for A than B and C (p less than 0.05) at 48 hours post muscle soreness bout. These data indicate that pulsed ultrasound accelerates restoration of normal muscle performance, and thus is effective in decreasing delayed onset of muscle soreness. The mechanism for decreasing soreness perception in the muscle is unknown, but may be related to decreasing intramuscular pressure and/or decreasing the inflammatory response.