PURPOSE: The differential effects on blood perfusion of the vasodilator hydralazine (HYD) between tumor and normal muscle have been measured using the dynamic enhanced-magnetic resonance imaging (DE-MRI) technique. METHODS AND MATERIALS: DE-MRI is a noninvasive method of determining blood perfusion in tumors and normal tissues using the MR contrast agent Gd-DTPA. Hydralazine is currently being used in an attempt to increase tumor response to bioreductive agents and to hyperthermia. RESULTS: We show that a dose of 1.2 mg/kg HYD causes an increase in tumor perfusion while doses > or = 2.5 mg/kg cause a decrease in tumor perfusion. The latter was accompanied by a dose-dependent increase in normal muscle perfusion consistent with the "steal effect." CONCLUSION: This study demonstrates the sensitivity of the DE-MRI technique and its capability of providing estimates of blood perfusion in normal and tumor tissue as well as in smaller regions of a solid tumor. Such features would make it clinically useful in the study of tumor response to radiation therapy and chemotherapy in patients.