Free amino acids, total methylated onium compounds (TMOC) and total nitrogen were investigated in young and old leaves of 22 mangrove species from Northern Queensland (Australia). Total nitrogen ranged between 0.35 to 2.5 % of dry matter depending on leaf age and species. The soluble nitrogen compounds accounted only in a few cases for more than 10 % of the total nitrogen. High proline accumulation was observed in only three species: Aegialitis annulata (28.5 mol· m -3 plant water), Xylocarpus granatum (76.0 mol· m-3 pw) and Xylocarpus mekongensis (56.7 mol· m -3 pw). The latter two species contained also hydroxyproline as a major component of the amino acid fraction. GABA, GLU, ASP and ALA were the most frequently occurring amino acids in the other species. A vicennia eucalypti/olia, A vicennia mao rina, Hibiscus tiliaceus and Heritiera littoralis accumulated high concentrations of TMOC (up to 107 mol· m -3 plant water), while Acanthus ilici/olius stored both TMOC and PRO.The occurrence of organic solutes in mangroves is discussed in comparison to herbaceous halophytes.