Abstract: A method and apparatus for in vivo electroporation therapy. Using electroporation therapy (EPT) as described, tumors treated by a combination of electroporation using the apparatus and a chemotherapeutic agent caused regression of tumors in vivo. In one embodiment, a method of EPT utilizes low voltage and long pulse length for inducing cell death. One embodiment includes a system for clinical electroporation that includes a needle array electrode having a "keying" element that determines the set point of the therapy voltage pulse and/or selectable array switching patterns. A number of electrode applicator designs permit access to and treatment of a variety of tissue sites. Another embodiment provides a laparoscopic needle applicator that is preferably combined with an endoscope for minimally invasive EPT.