Abstract To study the feasibility and optimum conditions for thermal ablation of prescribed tissue volumes in animal tumour models we have built and applied experimentally two exposure systems. Both operate at either 0.57 MHz (fundamental) or 1.7 MHz (third harmonic), with an aperture of ≈100 mm and a focal length of 150 mm. One system uses acoustic lens focusing and the other a spherical bowl transducer. When required, the lesioning geometry can be precisely coordinated with ultrasonic image information derived from a Siemens Sonoline system 1 1 ter Haar, G.R., Clark, R.L., Vaughan, M.G. and Hill, C.R. Trackless surgery using focussed ultrasound: technique and case report J Minimal Invasive Ther. (1991) 1 13–19 .