The kinetics of the formation and deoxygenation of oxyhemerythrin and oxyhemocyanin was investigated by T-jump and stopped-flow methods as a function of pressure. For hemerythrin the activation volumes Delta V-on(double dagger) = +13.3 +/- 1.1 cm(3) mol(-1) and Delta V-off(double dagger) = + 52.2 +/- 0.7 cm(3) mol(-1) were obtained. These values give a reaction volume <(Delta)over bar V> = -39 +/- 2 cm(3) mol(-1) for the hemerythrin/dioxygen system. With these volume data a volume profile was constructed, A comparison with the volume profile fdr the same reaction of myoglobin shows their similarity but with the difference that the volume data for hemerythrin are twice as large as for myoglobin. In contrast hemocyanin did not show a pressure-dependent uptake of dioxygen. The pressure dependence of the deoxygenation of oxyhemocyanin could not be measured. The reaction mechanisms for the formation and deoxygenation of the oxygen carrier proteins are discussed in a comparative way.