The treatment of GOTO cells, originated from human neuroblastoma, with recombinant human interferon-gamma (rHuIFN-gamma) induced the morphological changes: the extension and bifurcation of neurites and the multinucleated giant cell formation. The treatment of KP-N-RT cells, originated from human neuroblastoma, with rHuIFN-gamma also induced the similar morphological changes. The treatment of these cells with natural HuIFN-gamma also induced the same morphological changes, but those with recombinant human leukocyte interferon (rHuIFN-alpha A), recombinant human fibroblast interferon (rHuIFN-beta) and recombinant murine interferon-gamma (rMuIFN-gamma) did not induce it. The rHuIFN-gamma and the rHuIFN-beta inhibited more strongly the growth of GOTO and KP-N-RT cells than the rHuIFN-alpha A. This suggests that the morphological changes of these neuroblastoma cells are not simply due to the cell growth inhibition, but due to the property which only the rHuIFN-gamma possesses.