The effect of recombinant human interferon gamma (IFN-gamma) on the induction of HLA class II (HLA-DR, -DP, -DQ) antigen expression on human corneal epithelial (HCE) cells was examined in different stages of culture. Primary cultures were established with limbal explants without endothelium. HCE cells in Stage 1 and Stage 2, with cells negative and positive for the 64K corneal keratin (the marker for advanced corneal epithelial differentiation), respectively, were prepared. HCE cells in both stages were treated with IFN-gamma at a concentration of 0 to 1000 U/ml for two to six days and were stained by the avidin-biotin peroxidase complex method. Class II antigens were not detected on HCE cells in either stage without IFN-gamma treatment. IFN-gamma induced three class II antigens on HCE cells in both stages in a dose- and time-dependent manner but at different levels for each antigen (DR greater than DP greater than DQ). In addition, DQ expression was related to cell differentiation, with DQ extremely rare at Stage 1 and more frequent at Stage 2 (5% vs. 20%). These findings indicate that the induction of class II antigens on HCE cells may be regulated by IFN-gamma independently for each of the antigens and that DQ induction may depend upon the differentiation of HCE cells in culture.