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A rapid staining method using auramine O and acridine orange (AOAO) is described for staining mycobacteria and fungi in paraffin sections of bovine tissues. One hundred seventy-seven tissue sections from specimens divided into two general groups on the basis of previous histopathology results were examined with a fluorscent microscope. Group I, a total of 77 sections, were from 47 mycobacterial and 30 fungal granulomas. Mycobacteria were found by the AOAO procedure in 44 of the 47 tissues previously diagnosed as positive for mycobacteria. All 30 fungal granulomas previously diagnosed using convential fungal stains were positive with the AOAO procedure. Group II consisted of sections prepared from 100 granulomas in which typical mycobacterial lesions were observed by histopathologic examination but in which no mycobacteria had been detected. Using the AOAO procedure, two of these 100 granulomas were found to contain mycobacteria and two were found to contain bacterial colonies. In the remaining 96 no etiologic agent could be demonstrated.