Modulation of the growth of human pancreatic cancer cell lines in vitro by recombinant human tumor necrosis factor-alpha (TNF-alpha) and recombinant human interferon-gamma (IFN-gamma) was investigated. TNF-alpha exerted antiproliferative effects on three of nine pancreatic cancer cell lines and WiDR colorectal cancer cells. When administered together with IFN-gamma TNF-alpha showed enhanced antiproliferative effects on a subset of the pancreatic cancer cell lines tested, including those found to be insensitive to treatment with TNF-alpha alone. Thus the antiproliferative effect achieved by a combined treatment with TNF-alpha and IFN-gamma exceeded that observed with either drug alone in seven of nine pancreatic cancer cell lines.