The effect of electric pulses on tumour blood flow was investigated in the murine fibrosarcoma SA-1. After the application of short intense electric pulses, relative tumour perfusion was measured using an 86RbC1 extraction technique. A significant reduction of tumour perfusion (approximately 30% of control) was observed within 1 h following the application of eight electric pulses to the tumour. Thereafter, tumour blood flow slowly recovered, almost reaching the pretreatment level by 24 h. No change in perfusion was induced in the untreated contralateral normal leg muscle. A similar pattern of blood flow reduction was induced when a second set of electric pulses was applied to the tumour following a 24 h interval. The degree of tumour blood flow reduction was dependent upon the number of electric pulses applied, at 1040 V, and less effect was observed if less than eight pulses were applied. A modification of the amplitude of the electric pulses resulted in changes in the direction of tumour blood flow response. Tumour blood flow increased following pulses in the range between 80 and 560 V and decreased at amplitudes higher than 640 V. These results demonstrate that the local application of electric pulses to solid tumours can modify tumour blood flow. Pulses of increased amplitude resulted in the progressive reduction of tumour blood flow with a corresponding increase in tumour cytotoxicity as measured by growth delay. Tumour blood flow reduction by electric pulses could have potential in exploiting modalities mediated by tumour hypoxia, e.g. activation of bioreductive agents.