Electroporation -mediated gene transfer relies upon direct delivery of plasmids into cells permeabilized by electric fields, a method more efficient than transfer using nonviral vectors, although neither approaches the transfer efficiency of viral vectors. Here we studied electrotransfer of a gene encoding an angiogenesis inhibitor ( endostatin ) into primary tumors and muscle tissues, which would serve as a site of synthesis and secretion into the bloodstream of a therapeutic antimetastatic protein with systemic effects. Optimum electroporation conditions ( voltage, number and duration of impulses, separation of caliper electrodes ) were first established to maximize expression of a reporter gene transferred into murine Renca kidney carcinoma, B16( F10 ) melanoma, or skeletal muscle tissues. In neoplastic tissues, electrotransfer of plasmid DNA was far more efficient than electroporation with lipoplexes, but no differences between naked DNA and lipoplexes were found in case of electroporated muscles. We then studied the electrotransfer of plasmid DNA carrying the endostatin gene into pre -established experimental Renca tumors. A significant inhibition of tumor growth was observed in animals electroporated with this construct. Electrotransfer of the endostatin gene into muscle tissues resulted in reduced numbers of experimental B16( F10 ) metastases in the lungs. This study clearly shows that electroporation may be used to efficiently transfer antiangiogenic genes into both normal and neoplastic tissues.