Acacia rigidula Benth., blackbrush, is a shrub found growing on rocky ridges in west and southwest Texas and northern Mexico. Consumption of blackbrush and a related species guajillo, Acacia berlandieri Benth., has been associated with a locomotor ataxia known as 'limber leg'. In an effort to identify the mechanism of this toxicity, blackbrush was subjected to rigorous chemical analysis. In addition to the four previously detected amines, N-methyl-β-phenethylamine, tyramine, N-methyltyramine, and hordenine, 40 other alkaloids and amines were isolated and identified by GC- MS. These alkaloids and amines included nicotine, N,N-dimethyltryptamine, mescaline, several tetrahydroisoquinoline alkaloids, and four amphetamines. A significant increase in the number and relative quantities of these compounds was observed in late season foliage.