The ability of retinoic acid (RA) to upregulate gene expression in human tumor-infiltrating lymphocytes (TIL) transduced with a Moloney murine leukemia virus containing the cDNA encoding tumor necrosis factor (TNF) has been studied. TNF production was increased approximately twofold after treatment with RA. This increase was dose dependent and corresponded to a rise in the level of LTR-driven mRNA measured by Northern analysis. RA did not appreciably increase transcription by the SV40 promoter or increase endogenous TNF production. The effect lasted for 3-6 days following withdrawal of RA. These studies indicate that RA can upregulate LTR-driven gene expression in TIL cells bearing retroviral vectors and may thus be of use in studies of the gene therapy of cancer.