Aerial parts of 63 flowering plant species distributed in 43 genera and 22 families have been examined for the presence of betaines and tertiary sulphonium compounds. The plants tested were collected primarily either from salt marshes or close to the sea, but other species in either the same genus or family as plants collected from the coastal area were included in the study. Betaines were isolated from all but six of the species collected, but tertiary sulphonium compounds were not detected in any. High concentrations of betaines were found in all species of Chenopodiaceae examined as well as in 12 other species in other families, most notably Sesuvium portulacastrum (Aizoaceae), Avicennia marina (Verbenaceae) and Spartina townsendii (Gramineae). Most of the species tested contained betaines in low concentrations (0.0009-0.10% dry weight). The qualitative distribution of betaines within different species of any one genus was consistently the same.