The metabolic responses of eucalyptus and safflower cells to hydrodynamic stress in a 550-cm(3) stirred tank reactor were investigated. At 0.5 - 2.3 m(2)/s(3) of energy dissipation rate, the decreases in respiration rate and ATP content were larger than the decrease in the membrane integrity. Intracellular NAD(P)H was decreased and cytosolic calcium content was increased by agitation. EGTA, verapamil and W-7 suppressed the decrease in NAD(P)H. These results suggest that the cytosolic calcium, as a second messenger, mediate the signal of the hydrodynamic stress into the metabolism which induces the decrease in respiration rate. Furthermore, a decrease in the filamentous actin content due to agitation was observed.