Leukotoxin, cis-9,10-epoxyoctadeca-12(Z)-enoic acid (LTX), and isoleukotoxin, cis -12,13-epoxyoctadeca-9(Z)-enoic acid (iLTX), are the monoepoxides of linoleic acid (cis-9,12-octadecadienoic acid). In the systems so far examined two primary metabolites are LTX diol, threo-9,10-dihydroxy-octadeca-12(Z)-enoic acid, and iLTX diol, threo-12,13-dihydroxyoctadeca-9 (Z)-enoic acid. See figure 1. The first mention of LTX, per se, in the literature was in 1986 (1), but the two isomers of epoxyoctadecenoic acid have been discussed since before dy1971. LTX and iLTX are found endogenously in both animals and plants. While their defensive role in plants seems fairly well established (2), their role in animals is less clear. What is clear is that LTX and iLTX are formed from linoleic acid, usually when the organism is under less than optimal conditions, and that they have a wide range of effects.