The immunoregulatory effects of human recombinant transforming growth factor (rTGF) beta 1 and human recombinant glioblastoma-derived T cell suppressor factor (rG-TsF)/TGF beta 2 was investigated in mice infected with lymphocytic choriomeningitis virus (LCMV) or vaccinia virus. Starting on the day of infection, i.p. injections of 1 microgram/day or rTGF-beta 1 or rG-TsF/TGF-beta 2 suppressed the generation of virus specific CTL. The effect of TGF-beta on CTL (day 8) was less pronounced when TGF-beta treatment was delayed for 3 days after LCMV infection. rG-TsF/TGF-beta 2 also has an inhibiting effect on CTL-mediated disease in LCMV-infected mice: it prolonged the survival time of mice infected with LCMV and reduced the local swelling reaction after infection into the footpad. These results indicate that rTGF-beta 1 and rG-TsF/TGF-beta 2 influence T cell immune reactivity in vivo.