Taenia multiceps is a taeniid cestode that in its adult stage lives in the small intestine of dogs and other canids. In the intermediate hosts, the larval stage of T. multiceps causes coenurosis, a common disease in the CNS of ruminants, which typically leads to the death of the infected animals. Recent research into new methods for control of coenurosis and other taeniid cestode infections such as hydatidosis has identified vaccination as a potentially valuable new tool. In order to test the applicability of vaccination as an approach for control of T. multiceps infection in sheep, a field trial was carried out against natural infection in Sardinian farms (Italy) with recombinant proteins of T. multiceps. The recombinant proteins with Quil A as adjuvant were injected subcutaneously, the first administered to lambs at 10-12 weeks of age and a booster dose given after 2-4 weeks. A total of 632 sheep were selected, belonging to the "replacement quota" of six different farms, of which 424 were used as controls (unvaccinated) and 208 were vaccinated. After a period of more than 40 months from the beginning of the field trial, 33 episodes of cerebral coenurosis occurred in the monitored farms, including 32 cases in control sheep and l case in a vaccinated animal. Statistical analysis revealed a significant reduction in the number of coenurosis cases in the vaccinated animals (chi(2)=14.08, P<0.001). This is the first successful field test of a practical vaccine against T. multiceps and, considering the high degree of effectiveness achieved, could be a prelude to routine application in field situations of particular risk, such as Sardinia.