The occurrence of glycine betaine and γ-aminobutyric acid betaine extracted from the macroalgal species Ulva lactuca (Ulvophyceae), Cystoseira humilis, Fucus spiralis, Fucus vesiculosus (Phaeophyceae) and Gelidium sesquipedale (Rhodophyceae), growing on the Atlantic Moroccan coast was investigated. Seaweed extracts analyzed by TLC showed that all the species contained glycine betaine, but γ-aminobutyric acid betaine was detected only in members of the classes Fucaceae and Gelidiaceae. Extracts of Gelidium sesquipedale contained glycine betaine, γ-amino butyric acid betaine and α-alanine betaine. Extracts of Cystoseira humilis (myriophylloides) contained glycine betaine only, while Ulva lactuca extract contained glycine betaine and α-alanine betaine.Within the Phaeophyceae, yields of these compounds were consistently higher in the Fucaceae than in Cystoseiraceae. High performance liquid chromatography using short wavelength ultra-violet radiation detection was found to be unsuitable for the analysis of betaines in seaweed extracts, even after partial purification by passage through ion-exchange columns. Analysis by 1H NMR spectroscopic methods confirmed the presence of glycine betaine, γ-amino butyric acid betaine and α-alanine betaine in the seaweed extracts.