The phospholipid composition of two species of infusorians (Ciliophora) has been investigated. It has been shown that the alkyl form is present in the phosphatidylethanolamines and their phosphonic analogs, and in the phosphatidylcholine, phosphatidylserine, and phosphatidylinositol. The main fatty acid in the total lipid extracts was arachidonic. The main alkyl ethers of glycerol were batyl and selachyl alcohols. It has been shown that free-living infusorians may form promising materials for an all-sided study of the metabolism of alkyl-containing glycerophospholipids and sources for their preparative isolation.