OBJECTIVE: To measure tissue-temperature rise in the lateral aspect of the ankle during 10-minute ultrasound treatments with ultrasound gel (gel), a gel pad with a thin layer of ultrasound gel on the top (gel/pad), and a gel pad with a thin layer of ultrasound gel on the top and the bottom coated with ultrasound gel (gel/pad/gel). DESIGN AND SETTING: We used a 1 x 3 repeated-measures, crossover design. The dependent variables were tissue-temperature change and time to peak temperature. The independent variable was the type of ultrasound coupling medium. Treatment orders were randomly assigned, and all possible orders were assigned 3 times. A thermocouple was inserted through a 32-mm catheter at a depth of 1 cm into the target-tissue space, the posterior lateral aspect of the left ankle, halfway between the lateral malleolus and the Achilles tendon. Each treatment consisted of ultrasound delivered topically at 1 W/cm(2), 3 MHz, in the continuous mode for 10 minutes. SUBJECTS: Eighteen healthy, college-aged student volunteers (13 women, 5 men), with no history of ankle injury in the previous 6 months. MEASUREMENTS: Intratissue temperature, measured every 30 seconds for 10 minutes. RESULTS: Intratissue temperature increases during the 10-minute treatments were significantly greater for the ultrasound gel (7.72 degrees C +/- 0.52 degrees C) and the gel/pad/gel (6.68 degrees C +/- 0.52 degrees C) than for the gel/pad (4.98 degrees C +/- 0.52 degrees C). CONCLUSIONS: When ultrasound is applied over bony prominences, a gel pad should be covered with ultrasound gel on both sides to ensure optimal heating.