The purpose of this investigation was to determine the effect of ultrasound intensity and mode on serum salicylate levels following phonophoresis. Approximately 12-13 g of a salicylate product (Myoflex) was applied to the right anterior forearm of five males and two females. Randomly ordered ultrasound treatment intensities (0.0 W.cm-2; 1.5 W.cm-2, pulsed 50%; and 1.5 W.cm-2, continuous) were applied through the salicylate-containing product for a 5 min duration. A 7.0 ml blood sample was drawn from the left anterior forearm prior to each treatment and again 2 h after treatment. Analysis of variance indicated that none of the topical salicylate treatments produced an increase in serum salicylate levels. These findings suggest that there is no appreciable absorption of salicylate into the bloodstream following topical application of salicylate with or without the use of ultrasound. Since any penetration of salicylate through the skin would result in an increase in serum salicylate levels, the efficacy of phonophoresis to introduce medication into the subdermal tissue is questionable. These findings suggest that a critical review of phonophoresis in general is indicated.