A recombinant form of the endogenous heterodimeric cytokine interleukin-12 with potential antineoplastic activity. Recombinant interleukin-12 binds to and activates its cell-surface receptor, stimulating the production of interferon-gamma (IFN) which, in turn, induces IFN-gamma-inducible protein-10 (IP-10) and so inhibits tumor angiogenesis.