cis-9,10-Methyleneoctadecanoic acid methyl ester is a cyclopropane fatty acid methyl ester.1 It stimulates DNA synthesis in rat hepatocytes. cis-9,10-Methyleneoctadecanoic acid methyl ester has been used as a standard for the quantification of cis-9,10-methyleneoctadecanoic acid in bacterial membranes by co-chromatography.2