67Ga imaging was used in a group of 13 untreated patients with documented South American blastomycosis in an attempt to obtain additional information on the site and extent of the lesions. All diagnoses were confirmed by demonstration of the fungi in the lesions or body fluids. Serologic tests were performed on all patients. 67Ga imaging was correlated with X-ray in all patients, and with bone imaging when bony lesions were suspected. 67Ga imaging was positive for all lesions detected on chest X-ray and by clinical evaluation. More importantly, lesions clinically unsuspected and missed by other diagnostic techniques were shown on 67Ga imaging: bony and hepatic lesions in three patients; a brain lesion in one patient and parotid gland involvement in five patients. There was good agreement between 67Ga imaging and clinical and laboratory data, scintigraphy being more sensitive. Follow-up studies after specific therapy demonstrated decreased uptake in the lungs and other sites. 67Ga imaging is a useful tool for detection of suspected and unsuspected lesions of blastomycosis and to evaluate the response of the disease to specific therapy.