Autologous mixed lymphocyte-tumor cell cultures (MLTC) were initiated with cytokine (IFN gamma and TNF alpha)-treated ex-vivo tumor cells of lung, ovarian, breast and stomach carcinomas. The cytokine-treated tumors expressed class-I but not class-II molecules. Although the proportion of CD8+ lymphocytes increased in the bulk culture of MLTCs, in 5/7 experiments the majority of the established T-cell clones were CD4+. Among the CD8+ clones a high proportion (77%) was cytotoxic, while the proliferative response was more frequent among the CD4+ clones (70%). In 4/26 cytotoxic T-lymphocyte (CTL) clones (3/17 CD4+ and 1/9 CD8+), derived from a patient with class I+ class II- stomach carcinoma, lysis was restricted to the autologous tumor cells. These auto-tumor-specific clones did not lyse the autologous ConA blasts, the 5 allogeneic ex-vivo tumors, the NK-sensitive K562 or the relatively sensitive Daudi cells. The cytotoxicity of these clones was inhibited by pre-incubation of the tumor cells with W6/32 (alpha-class I) MAb, or by preincubation of the lymphocytes with OKT3 (alpha-CD3) MAb. The alpha-CD4 (OKT4) MAb had only a marginal effect on the CD4+ clones, while the lytic function of the CD8+ clone was inhibited by the alpha-CD8 (OKT8) MAb. The 3 CD4+ CTL clones also responded with proliferation to the autologous tumor cells. This proliferative response was inhibited by the presence of W6/32 MAb. Our results indicate that the auto-tumor lysis exerted by CD4+ CTL clones was restricted by the class-I antigens, and that the CD4 molecules of the clones were not essential for the lytic interaction.