Lipoxygenases are found widely in plants, fungi, and animals (1-5). The suitable substrates are polyunsaturated fatty acids containing a series of cisdouble bonds. These are the essential fatty acids in humans. These substrates are not present in most bacteria (cyanobacteria and some marine species excepted (6, 7)), and yeast also lack the necessary desaturases for their synthesis. In accord with this absence of substrate, there is no lipoxygenase in the yeast genome (Saccharomyces cerevisiae), and lipoxygenases are also absent from typical prokaryotes. There is no definitive account of a lipoxygenase in insects, although a typical arachidonic acid-derived lipoxygenase product (hydroxyeicosatetraenoic acid (HETE)1) is identified in the primitive insect Thermobia domestica (8). There is a lipoxygenase in the unicellular Chlorella (9) and a partial lipoxygenase cDNA sequence in the data bases from the slime moldDictyostelium discoideum. Higher plants contain multiple lipoxygenases with at least eight identified in soybean, Glycine max. In the mouse there are seven genes that express lipoxygenase proteins, and five homologues (and an expressed pseudogene) are characterized in humans (10-12).