Ethyl linolenate (Wijs iodine number 247.3; theory 248.5) was prepared by the debromination of purified hexabromostearic acid. The thiocyanogen value determined exactly as recommended by the Committee on Analysis of Commercial Fats and Oils, [Ind. Eng. Chem. Anal. Ed.8: 234 (1936)] was found to be 151.2, corresponding to a corrected value of 167.3 for the free linolenic acid, rather than the theoretical value of 182.5. Data are presented to show the effects of time, excess and concentration of reagent. The thiocyanogen number of linolenic acid is proved to be an empirical value which, however, is reproducible under carefully controlled conditions. Several improvements of technique found to insure reproductibility of results are discussed in detail.