Abstract. The cellular effects of pulsed and continuous ultrasound on the protein content of muscle after trauma were determined in this study. Rats were subjected to a single impact trauma to the gastrocnemius. Six major treatment groups were employed: (1) uninjured control, (2) injured control, (3) & (4) uninjured ultrasound treated, and (5) & (6) injured ultrasound treated. The ultrasound treated groups were subdivided into continuous ultrasound, and pulsed ultrasound treatments (dosage = 1.0 watts/cm 2 × 5 min), which were given from day 2 to day 7 post-trauma once daily. Animals were sacrificed at 1, 3 and 7 days, the medial gastrocnemius muscle being dissected and solubilized for protein content determination. On day 7 the control injured group had a statistically greater mean protein content than the injured continuous ultrasound treatment group, and the mean protein content of the injured pulsed ultrasound treatment group was statistically greater than both the injured control or the injured continuous ultrasound treatment groups (one way ANOVA, P<0.05). The means of all three uninjured control groups were not significantly different at day 1 or 7. Within each group, only the control injured (18% or 44 mg increase ± 17 mg) and the injured pulsed ultrasound treatment (7% or 22 mg increase ± 9 mg) groups showed statistically significant changes (95% Confidence Interval) in protein content from day 1 to day 7. All other treatment groups showed no statistically significant increases.