Free amino acids in the seeds of 80 species of Acacia have been determined. In addition to confirming the known difference in seed amino acid 'patterns' shown by species of the series Gummiferae on the one hand and species of the series Phyllodineae and Botryocephalae on the other, we have found that species of the series Vulgares Benth. show two additional 'patterns' One of these is common to some of the Afro-Asian species of the series which have been analysed and the other is common to species from America and Africa. One of the 'marker' amino acids of the Afro-Asian group is the neurotoxic lathyrogen a-amino-ß-oxalylaminopropionic acid. The possible taxonomic and phylogenetic significance of these results is discussed, with special reference to five species A. ataxacantha, A. confuse, A. heterophylla, A. coulteri and A. kauaiensis.