A recombinant replication-defective adenovirus which encodes the gene for the cytokine human interferon-beta (IFN-beta). Once inserted into and replicating in host tumor cells, recombinant adenovirus-hIFN-beta expresses human IFN-beta, which may stimulate an antiproliferative natural killer (NK) cell response against tumor cells and induce caspase-mediated tumor cell apoptosis.