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Sato and Fieldsteel first described the nuclepore membrane filter method for concentration and quantitation of Mycobacterium leprae and proposed that the new method could be applied to detect M. leprae in quantities as few as less than 104 in many types of specimens.In this paper the authors present the results of their further tests on the nuclepore method comparing with the microspot and culture methods.A one-week culture of M. fortuitum in Dubos liquid was divided into alliquots of 10 portions and each portions was diluted in series. Comparative counts of acid-fast bacteria were made on 10-2 dilutions by the microspot method, on 10-4 by the nuclepore method and on 10-5 anb 10-6 by the culture method. As shown in Table 1, there was close correlation between the nuclepore method and the culture method. However, about two times of bacteria were counted by the microspot method more than by the other two methods.Cell culture fluids from M. leprae-infected cultures were examined by the microspot and nuclepore methods. It was clear from the data in Table 2 that the nuclepore method could detect M, leprae in quantities as small as 1.52×102 in specimens. This detection corresponded to approximately the same range as determined by the culture method on culturable mycobacteria.As mentioned above, the authors confimed the findings reported by Sato and Fieldsteel.