Low dosage regional streptokinase therapy has become increasingly popular as an alternative to surgical treatment in acute and chronic arterial occlusions. Success rates are reported between 70 and 100 per cent. This is surprising, considering the paucity of data in the literature regarding the type of lesion treated, objective criteria for good results and predictive factors of success. In a review of 22 acute and chronic arterial occlusions of the lower extremity treated with low dosage regional streptokinase, the outcomes were grouped as either favorable or unfavorable. A success rate of 36 per cent was achieved. The two outcome groups were compared with regard to pre-existing diseases or risk factors, indications for treatment, duration of symptoms or level of occlusion. No significant difference was found. With regard to pretreatment runoff, 100 per cent of the patients in the favorable outcome group were found to have good runoff as opposed to only 21 per cent of the patients in the unfavorable outcome group. Of the patients who also had PBD procedures, all of those in the favorable group had good runoff, and all in the unfavorable group had poor runoff. In nearly achieving statistical significance, a trend was noted establishing embolic lesions as more favorable than thrombotic lesions. We conclude that our low success rate with low dosage regional streptokinase therapy is due to our strict criteria for success and the nonselective nature of the patients we studied. As a result of these findings, we do not support the preferred use of low dosage regional streptokinase therapy in arterial occlusion. However, in patients who represent high surgical risks, a trial of low dosage streptokinase therapy seems indicated if favorable predictors of success, such as good pretreatment runoff, embolic lesion and mild symptoms, are present.