‘Without these tools (skin-test and complement fixation antigens for epidemiological, diagnostic, and prognostic use) we are at least 50 years behind in our defining of the disease blastomycosis’ (63). This statement by Rippon et al. emphasizes the need for a well defined antigen or group of antigens from Blastomyces dermatitidis, not only for the two tests named above, but for any serological or immunological test. Several different preparations have been reviewed which are beginning to approach the quality necessary for such a sensitive and specific antigenic tool. All of these require further characterization and, in most instances, purification. One purified fraction isolated from blastomycin, the F fraction, has shown exceptional promise as a skin-test agent in guinea pigs but has not been further studied. A 10–30K molecular weight fraction of the yeast cytoplasm has shown good reactivity, and contains a protein shown by PAGE to be common to several skin-reactive preparations. This fraction has not been further purified. An ASWS preparation has been partially characterized and shown to be especially sensitive and specific in animals, though not yet in humans. Purification of this fraction by PAGE has uncovered a highly reactive protein which may be related to one isolated from the cytoplasm. Investigations using this purified component have not been attempted in humans. The A antigen has been well characterized regarding its applicability to human diagnosis. It has been partially purified and two of its components associated with its reactivity. It also has probably the best possibility as an immediate serologic tool. Even here, though, current preparations contain much extraneous material which could conceivably create cross-reactivity problems in the future. The ethanol-precipitate antigens which have shown such superior results in the past have not been employed recently, nor have they been extensively characterized. This fraction may contain the reactive A antigen or other antigens deserving of study. Hopefully, the use of this technique can be encouraged as one starting point for isolation procedures. The importance and isolation of enzymes and mannose containing antigens have probably not received adequate attention. An almost uniform identification of mannose in reactive preparations argues for purification procedures based on its presence. Finally, use of hybridoma technology to produce antibodies specific for antigens of B. dermatitidis promises to improve our understanding of the organism and to help isolate purer antigenic fractions. The search for antigens of importance in the immunology of B. dermatitidis should not be confined to any one or all of the antigens discussed above. A variety of components will likely be necessary for complete understanding of the disease and for diagnostic use. It has been observed that ‘information of clinical value can be obtained from immunological reactions to several different antigens’ (35), thereby encouraging continuous efforts to obtain as many as possible.