We have presented data showing that IFN-beta at 1,000 U/mouse i.v. inhibits the generation of Ts-mediated tolerance to dinitrofluorobenzene (DNFB) and abrogates the transfer of suppression by Ts. We have also presented data showing that IFN-beta up to 10,000 U/mouse i.v. has no adverse effect on sensitization and elicitation. IFN-beta appears to be a suitable agent for evaluation as an adjunct in the immunotherapy of Ts inducing tumors.