In the course of screening research on alkaloids among metabolites of microorganisms, Streptomyces strain No. FFD-101 which was isolated from a soil sample collected in Bankok of Thailand, was found to produce a new alkaloid, nigrifactin both in its culture filtrate and mycelium. This alkaloid possessed strong inhibitory activity against histamine and caused a transient fall of blood pressure. From the results of taxonomical study on the strain No. FFD-101, it was found that this is a variant of Streptomyces nigrifaciens, to which the name, Streptomyces nigrifaciens var. FFD-101 was proposed. Examination of the alkaloid productivity with media in various compositions indicated that the medium containing glycerol 3% as carbon source and casamino acid 0.35% as nitrogen source was most suitable for the production. © 1970, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.