SYNOPSIS. The venoms of spiders are quite complex and contain an array of biologically active components. The majority of studies on the biochemical aspects of these venoms have utilized four species: Phoneutria fera, Lycosa erythrognatha, Atrax robustus , and Latrodectus mactans . They produce venoms which are lethal to mammals as well as arthropods. The following substances have been isolated from one or more of their venoms: a-aminobutyric acid, histamine, 5-hydroxytryptamine, spermine, proteases, hyaluronidase, phosphodiesterase, and toxic and lethal polypeptides. With the possible exception of spermine, the lethality of these venoms appears to be the result of the actions of the polypeptides. The other substances apparently play a subsidiary role.