1. 1. Cytochrome c oxidases from a number of eukaryotic organisms have been isolated and show spectral properties similar to those of the bovine enzyme. All possess both Cu and Fe atoms. 2. 2. Ultracentrifuge studies reveal that the camel oxidase is monomeric yet exhibits similar properties to the bovine enzyme. 3. 3. Investigations of the subunit composition have shown 7 subunits for all the species examined and similarities are suggested on the basis of the 203Hg labelling of the subunits. 4. 4. Steady state kinetic measurements show two kinetically functional cytochrome c binding sites on all the oxidases examined. The pH optima of the monomeric camel enzyme (pH 7.2) is significantly different to the dimeric bovine enzyme (pH 6.2). 5. 5. Pre-steady state measurements show a fast initial electron entry from ferrocytochrome c to ferricytochrome a followed by a slower second phase. These results are similar for all the oxidases studied and comparable to those already established for the bovine enzyme. 6. 6. A complete cycle of full reduction followed by oxidation by molecular oxygen leads to an activated ("pulsed") form of cytochrome oxidase. This property was exhibited by the enzymes from all the species examined. © 1981.