The time course of O2 consumption after acute salinity exposure (1, 3, 6, 12, and 24 h to 0, 7, 14, 21, 28, and 35 S) was examined in isolated supraesophageal ganglia, gills, and intact Macrobrachium olfersii (Wiegmann), a hyperosmoregulating freshwater palaemonid shrimp, to establish patterns of metabolic adjustment during salinity adaptation. In whole shrimps, O2 uptake rates decline with salinity increase to 21 S, subsequently increasing with further salinity increase. The rates increase to maxima after 6–12-h exposure in low salinities, decreasing steadily with time in high salinities. In gill preparations, O2 consumption rates increase to a maximum in 14 S, then decline; they are maximal after 3–6-h exposure to low salinities and diminish with time in high salinities. In the supraesophageal ganglion, rates of O2 uptake, always measured in seawater of 18 S, are also maximal when shrimps are exposed to 14 S, subsequently declining or levelling off. Rates decrease with time in shrimps exposed to very low salinities, and are stable in 21 S, reaching maxima after 3–6-h exposure of shrimps to all other media. Both tissues thus exhibit characteristic response patterns of O2 consumption rate which appear to depend on their functional significance within the context of the whole organism. Such data are interpreted to indicate an interrelationship between O2 consumption and osmoregulatory capability.