To extend our initial observation that recombinant gamma-interferon induced expression of class II major histocompatibility (HLA-DR) antigen on normal cultured human keratinocytes, we studied the antiproliferative effects of recombinant alpha- and gamma-interferons. Both interferons reduced the number of attached cells (dose range 10-10(3) units/ml; 7.1 X 10(-11) to 7.1 X 10(-9) M) and gamma-interferon was 100 times more potent than alpha. This effect did not require the presence of Langerhans cells. gamma-Interferon reduced total cell production during the first week without increasing the percentage of cells shed. During the second week, gamma-interferon also increased the percentage of cell shedding. Although 10(2) units/ml of gamma-interferon was maximal for HLA-DR expression by cultured keratinocytes, there was increasing reduction of attached cells between 10(2) to 10(3) units/ml. The demonstration that recombinant gamma-interferon induces HLA-DR expression and also inhibits keratinocyte proliferation in vitro at nanomolar concentration expands the growing list of normal cells whose biologic function may be influenced by this lymphokine in vivo.