1.1. The effect of salinity (0, 7, 14, 21, 28 and 35‰) on osmoregulatory capability and metabolic rate in adult Macrobrachium acanthurus, M. heterochirus, M. olfersii and M. potiuna, was investigated at 20°C using a microcryoscope and Warburg respirometer.2.2. All species are strong hyperosomotic regulators in freshwater or low salinities (0–14‰) while at high salinities (21–35‰), with the exception of M. olfersii, they are hypoconformers; M. olfersii exhibits a fair degree of hypo-osmotic regulatory capability.3.3. Isosmotic points decrease in the sequence M. heterochirus > M. acanthurus > M. olfersii > M. potiuna.4.4. For M. acanthurus and M. olfersii, the metabolism-salinity curves assume a dome shape with a high peak at 21‰ S, close to the isosmotic point. For M. heterochirus and M. potiuna, metabolic rates tended to decline with salinity increase.5.5. These results are discussed in relation to the distribution patterns of the adult shrimps and to physiological modifications occurring during development.