Although the use of low frequency ultrasound to enhance transdermal drug delivery (sonophoresis) was identified as effective in the 1990's, current understanding of the approach remains incomplete. This study aimed to improve knowledge in this relatively new technology. Initially, ultrasonic measurements were undertaken in order to check the output of the 20 kHz source used in all our research. Hydrophone measurements showed that the frequency was just 0.6% lower than the manufacturer's stated value. Use of a simple calorimetric method confirmed that the intensity varied in proportion to the generator's dial setting but that it was otherwise constant with time. Laser vibrometry confirmed good transducer performance.