Increasing the efficiency of gene transfer using non-viral vectors, which have the potential to be safe and economical, would improve upon available options for gene therapy. We previously reported that the third EGF motif of the extracellular matrix protein Del1 (E3) increases the transfection efficiency of non-viral vector methods. Here, we asked if E3 could increase the in vivo transfection efficiency of a polyplex-based approach. To test this, cDNA encoding a heat-stable alkaline phosphatase (AP) was first injected intravenously into mice along with recombinant E3. After 24 h, exogenous AP activity in serum was measured. We found that the introduction of E3 resulted in 50 % more AP activity as compared to the control. We next tested transfection into a tumour explant of SCCKN cells, an oral carcinoma-derived cell line. To do this, a cDNA encoding yellow fluorescent protein was locally injected into a tumour explant, followed by local injection of recombinant E3. Use of E3 increased the number of transfected cells to 2.5 times that of the control. Histochemical staining revealed that E3-induced apoptosis in a tumour explant. The data suggest that E3 might be a useful tool for cancer gene therapy using non-viral vectors.