RIBONUCLEASE A FAMILY, 1(Ribonuclease pancreatic) is an enzyme that in humans is encoded by the RNASE1 gene. By genomic sequence analysis, RNASE1 gene is mapped the to chromosome 14q11.2, where it is linked to 7 other RNase A superfamily genes. Monomeric human pancreatic RNase, devoid of any biological activity other than its RNA degrading ability, was engineered into a dimeric protein with a cytotoxic action on mouse and human tumor cells, but lacking any appreciable toxicity on mouse and human normal cells. This dimeric variant of human pancreas RNase selectively sensitizes to apoptotic death cells derived from a human thyroid tumor. Because of its selectivity for tumor cells, and because of its human origin, this protein represents a potentially very attractive, novel tool for anticancer therapy.