Sheep were immunized with a purified antigen (Hc-sL3) expressed on the surface of L3 larvae of the gastro-intestinal parasite, Haemonchus contortus, using different adjuvant and immunization routes. In the first experiment, intradermal immunization of sheep with Hc-sL3 and QuilA did not result in reductions in faecal egg counts after subsequent challenge infection while significant reductions were obtained when aluminium hydroxide (AH) was used as the adjuvant. Significant protection with Hc-sL3 absorbed on AH was confirmed in a second experiment and this protection was maintained when dextran sulphate was added to the Hc-sL3/AH mixture while the addition of pertussis toxin abrogated the protective effect. Significant levels of protection, as determined by reductions in both faecal egg counts and worm burdens, were also obtained when the Hc-sL3/AH mixture was injected into the rectal mucosa or the Hc-sL3 antigen was deposited on the surface of the rectal mucosa with cholera toxin. No correlations with antibody levels or isotype and protection were observed.