The seasonal distribution of fruiting myxobacteria, which are able to lyse cyanobacteria in the water and sediments of eutrophic lakes, was determined periodically in 1985 and 1986. Fruiting myxobacteria isolated from sediments of these sites were found to have a lytic effect on a wide variety of cyanobacteria. The myxobacterium isolate designated as S-1-8 was identified as Myxococcus fulvus Cohn. Lytic activity for cyanobacteria was produced during growth of the organism in a number of complex media. The maximal amount of activity was produced in casitone-yeast media and at the end of the log phase of growth.