The use of diagnostic ultrasound can be justified if it can be shown to provide only negligible or small risk while giving good benefit to the patient. In the absence of biological evidence, one way of assessing a new (or existing) piece of diagnostic equipment would be to predict the biophysical changes (i.e. heat and cavitation) that may be produced by its ultrasonic fields in tissue. An assessment of risk may then be made from our knowledge of thermal and cavitational biology. To this end, this study has sought to measure temperature rise, bubble formation, sonoluminescence and acoustic streaming arising from clinical transducers that have been carefully calibrated using a Beam Calibrator, and to determine whether there is good correlation between measured acoustic parameters in water and any of these biophysical characteristics. The results are inconclusive.