The effect of ultrasonic irradiation on the viability of normal and tumor cell cultures derived from human and mouse origins was investigated. The cells were irradiated with a frequency of 2 MHz and intensity of 0.33 W/cm2, up to 4 min and immediately tested for cell viability using four different parameters: vital staining for the determination of the rate of cell growth; [3H]-thymidine and [3H]-leucine incorporation as an indication of the rate of DNA and protein synthesis respectively; and cloning efficiency as a measurement of the cell ability to multiply. Two human normal cell lines used in our studies, FS11 foreskin fibroblasts and Wish cells, were relatively resistant to ultrasonic irradiation effect although the growth rate of the latter was somewhat affected, particularly after 2 or 4 min of irradiation. However, cells derived from either malignant melanoma or breast carcinoma were highly sensitive to irradiation as demonstrated by a reduction of 96% and 65%, respectively, in cloning efficiency even after irradiation for 1 min. A third tumor cell line derived from lung carcinoma was more resistant. Two normal clones derived from NIH/3T3 mouse fibroblasts were used. These clones revealed some degree of sensitivity, particularly after 4 min of irradiation. However, their murine-sarcoma-virus transformed counterparts were found to be even more sensitive at identical times of ultrasonic irradiation, although the differences are not as striking as demonstrated with cells from human origin.(ABSTRACT TRUNCATED AT 250 WORDS)