Salivary gland antigen, SGA, derived from partially engorged female Dermacentor andersoni was shown to be capable of inducing resistance to tick infestation in guinea pigs never previously exposed to ticks. Immunization regimens involved the administration of SGA by different routes and with or without the use of adjuvants. Induced resistance was expressed by significantly fewer larvae engorging, and the weight of larvae which did engorge was reduced. Salivary gland antigen has been shown to interact with the immune effector elements of animals which acquired and expressed tick resistance due to infestation. These findings demonstrated the potential for an immunologic approach to tick control.