Ultrasonically induced cell damage and active oxygen generation with 4-formyloximeetylidene-3-hydroxyl-2-vinyl-deuterio-porphynyl(IX)-6-7-diaspartic acid (ATX-S10) were compared in the same in vitro insonation setup. Sarcoma 180 cells suspended in air-saturated PBS were exposed to ultrasound at 2 MHz for up to 60 s in the presence and absence of ATX-S10. The viability was determined by Trypan blue exclusion test. Ultrasonically induced active oxygen generation in the presence and absence of ATX-S10 in air-saturated aqueous solutions of 50 mM 2,2,6,6-tetramethyl-4-piperidone was detected by electron spin resonance (ESR). Significant enhancement of the rates of both ultrasonically induced cell damage and nitroxide generation was demonstrated with 40-160 microM ATX-S10. Both rates correlated very well. The enhancement of both rates with ATX-S10 was suppressed by 10 mM histidine. These results suggest that ultrasonically generated active oxygen plays a primary role in the ultrasonically induced cell damage in the presence of ATX-S10.