SummaryInfection of cotton rats with Echinococcus multilocularis or vaccination with BCG, or its cell walls, activates peritoneal cells to kill the protoscolices of the parasite in vitro and protects laboratory animals against the cestode. To determine whether other ‘non‐specific’ stimuli would also protect against the parasite, cotton rat peritoneal cells were activated in vivo with PHA and transferred to recipients 3 days later. The recipients, controls and PHA‐treated animals were then inoculated with the parasite; 3 days after inoculation other untreated infected animals received cells activated in vivo with PHA. PHA‐activated cells, the PHA treatment itself and immunization with a homogenate of the parasite stimulated a leucocytosis and protected against infection by E. multilocularis; carrageenan abrogated protection in PHA‐treated animals. The results of this study confirm that protection against echinococcosis can be induced non‐specifically; these results suggest that immunity in hydatid disease may have an important component in the inflamma