We have previously reported preclinical studies in mice of the human mucin 1 (MUC1) antigen covalently linked to the yeast cell-wall mannan polysaccharide (MFP), and shown strong cellular responses of the T1 type using mice. We now describe the optimum parameters for administration of MFP to obtain cellular immunity [as measured by the cytotoxic T cell precursor (CTLp) frequency]. In dose/response studies, in which 1 microg-150 microg was given by the i.p. route, it was clear that doses of 1-7 microg led to cellular and not humoral immunity; at doses above 7 microg humoral immunity prevailed with little cellular immunity increasing doses giving greater amounts of antibody. The most favoured routes of administration were intraperitoneal or intradermal immunisation, which were substantially better than i.m., i.v.; s.c. administration was the worst. Three immunisations were necessary for a maximum cellular response, further immunisation decreasing the CTLp frequency. Six different adjuvants were used with MFP [complete and incomplete Freund’s adjuvant (CFA, IFA) Alum, Adjuprime, muramyl dipeptide (MDP) and glutaminyl-muramyl dipeptide (GMDP)]; Alum, GMDP, MDP and IFA moderately increased the CTLp frequency, IFA being the best. Even though preclinical studies of the immunogen in mice may not necessarily mirror the behaviour of the immunogen in humans, these studies demonstrate the factors to be taken into account for phase I/II clinical trials.