It has recently been shown that T-cell signal transduction molecules are altered in tumor-bearing mice. We have examined the expression of NF kappa B/Rel family proteins in T-cells from mice bearing Renca, a murine renal carcinoma. T-cells from Renca-bearing mice expressed undetectable levels of nuclear c-Rel, NF kappa B p65, and p50; however, two shorter forms of p50 (p48 and p46), truncated at the NH2-terminus, were present exclusively in the nucleus and were able to bind DNA. These T-cells have reduced expression of gamma-interferon mRNA. In mice successfully treated with flavone 8-acetic acid and recombinant human interleukin 2, the T-cells expressed normal levels of all three nuclear NF kappa B/Rel proteins. These results suggest that alterations in transcription factors may accompany changes in signal transduction molecules in T-cells from tumor-bearing animals; however, the changes are reversed with successful biological therapy.