Chlorination of oleic acid gave mainly 9,10-dichlorosteraic acid but other products were also formed. By-products included the dimer, 9(10)-(9,10-dichlorostearolyoxy)-10(9)-chlorostearic acid, and the related trimer, formed independent of temperature in the range examined (−20 to +29 C). Higher solvent-oleic acid ratios decreased the amounts of dimer and trimer; chlorination in the presence of hydrogen chloride did not. The equivalent weight of 9,10-dichlorostearic acid was found to increase markedly upon treatment with chlorine and light, but in the dark the acid was apparently unchanged. These effects were independent of temperatur