The acoustical fields produced by a variety of focused axisymmetrically curved surface transducers with large aperture have been investigated on the basis of Fresnel-Kirchhoff diffraction theory. The interrelation of ultrasound characteristics with some structural aspects of the transducers has been calculated and compared. The forms of resulting intensity maxima and their resulting suitability for surgical lesion of tissues are compared through parameters such as "lesioning capability" and "focussing efficiency." Although only modest changes in intensity distribution are possible, some may have applications in making lesions for control of focal cancer and other pathologies.