Under normal growth conditions, the human lymphoblastoid cell line Daudi expresses high levels of c-myc mRNA. These cells are also sensitive to growth inhibition by interferons. We have compared the levels of mRNA for the c-myc in untreated and human beta interferon (IFN-beta)-treated Daudi cells by RNA dot-blot and blot-hybridization analysis methods. Using a synthetic oligonucleotide complementary to the human c-myc mRNA as the probe, we detected a more than 75% reduction in the c-myc hybridizable poly(A)+ RNA in the IFN-beta-treated cells. This reduction in the c-myc mRNA appears to be selective because the level of actin mRNA is not significantly affected by the IFN-beta treatment. In addition, neither in vitro translation of mRNA extracted from IFN-beta-treated cells nor in vivo synthesis of cellular proteins in IFN-beta-treated cells are quantitatively affected. We surmise that the selective reduction in the amount of c-myc mRNA in IFN-beta-treated Daudi cells may be related to the IFN-induced inhibition of the Daudi tumor cell growth.