This report describes the effect of high energy shock waves (HESW) generated by a Siemens Lithostar on four human prostatic carcinoma cell lines in vitro. The effects of temperature, shock wave energy, cell density and the number of HESW were investigated. Pressure measurements were carried out in the focus of the lithotriptor and inside test tubes that were placed in the focus. Direct cell kill was inversely related to temperature, whereas a linear relationship was found with shock wave energy. Cell kill appeared to be independent of cell density. All four cell lines were sensitive to the treatment with HESW, but displayed a different dose-response pattern. In vitro treatment of PC-3 cells retarded their growth upon injection into nude mice. It is concluded that human prostatic tumour cells are killed by HESW. Therefore, HESW could be of potential value in tumour treatment.