A number of cytokines were tested for their ability to modulate HLA-DR antigen expression on normal human monocytes. IL 4, GM-CSF as well as IFN-gamma were able to increase HLA-DR antigen expression on monocytes. IFN-alpha was also able to augment HLA-DR antigen expression, but to a lesser degree. M-CSF, TNF-A, TNF-beta and IL 6 were not able to augment HLA-DR antigen expression. There were distinct patterns in the ability of different cytokines to augment class II histocompatibility antigen expression. IL 4 and GM-CSF selectively increased only HLA-DR and HLA-DP, but did not increase HLA-DQ antigens on monocytes. IFN-gamma, however, was able to augment the expression of HIA-DR, HLA-DP and HLA-DQ antigens. Combinations of IFN-gamma with either IL 4 or GM-CSF did not show any synergy for the augmentation of any of the class II antigens on monocytes.