The distributions and recoveries of the hemolytic activities and quantities of protein of complement components during cold ethanol fractionation were studied. Most of the components were recovered in Cohn's fraction III, with slight activities in fractions I and IV. The hemolytic activities of C1 and C5 were recovered in high yields in fraction III. The recoveries of activities of late components of complement (C6-C9) in fraction II + III were also high. These results suggest that many complement components can be isolated from Cohn's ethanol fractions.