Two recombinant mouse mammary tumor virus (MMTV) subunit vaccines have been constructed, in which linear sequences of the envelope gp 52 glycoprotein (EP3) or the superantigen (SAg) have been fused to single or multiple repeats of a T-cell epitope (P30) from tetanus toxin. Histidine tags or glutathione-S-transferase (GST) sequences have been included in the recombinant peptides in order to facilitate their purification by affinity chromatography. The EP3 or SAg recombinant polypeptides with four, one, or no T-cell epitopes were expressed in Escherichia coli, purified and injected intramuscularly, with non-ionic block copolymers as an adjuvant, into BALB/c mice. Following one or two boosts, the B- and T-cell responses against the recombinant proteins were analysed. The addition of T-cell epitopes considerably increased the immunogenicity of the subunit vaccines. The anti-EP3 response was maximum with four T-cell epitopes, while a single T epitope was optimal for the anti-SAg response.