A most compelling stimulus to investigate the influence of actively-induced immunity in experimental coccidioidomycosis is found in the epidemiologic studies ofSmith (35) andSmith et al. (37–39). Their serologic and skin test surveys among residents in areas of coccidioidal endemicity directed attention to a role apparently played by actively-acquired immunity in man exposed toCoccidioides immitis. It was found that after recovery from illness, or after the acquisition of dermal sensitivity to coccidioidin in the absence of manifest illness, there was very little likelihood of a second symptomatic coccidioidal episode.Smith (personal communication) inferred from the above observation thatC. immitis was endowed with effective immunogens and speculated (37) that live or killed coccidioidal vaccines could be of profound public health significance. During the two decades following the report ofSmith et al. (39) on the use of coccidioidin, workers explored the efficacies and advantages of live and killed vaccines in experimentally produced coccidioidomycosis in animals.