Summary and Conclusions: Repeated intradermal testing of negative reactors with coccidioidin alone does not ordinarily induce delayed sensitivity to this material. Repeated intradermal coccidioidin testing of reactors with weak or latent sensitivity may effect an anamnestic delayed reactivity to this material. Healthy subjects living in an area endemic for coccidioidomycosis may exhibit delayed allergy to coccidioidin in the absence of detectable serum complement-fixing antibody, and, occasionally, serum antibody may be present in such subjects without delayed allergy to coccidioidin. The above findings suggest that the delayed type of allergic inflammatory response to coccidioidin need not necessarily be correlated with the presence or absence of serum antibody—an expression of another parellelism between fungal hypersensitivity and bacterial allergy of the tuberculin type.