Although particulate fractions prepared from two colorless members of the Cyanophyta were shown by Webster and Hackett (1966) to possess NADH oxidase, it was recently reported that no NADH oxidase activity could be detected in particles isolated from some pigmented members of the Cyanophyta (Smith et al., 1967). This communication reports the results of studies on two pigmented and one colorless member of the Cyanophyta. Particles prepared from all three organisms possessed NADH oxidase activity, but lacked other respiratory activities e.g. cytochrome c oxidase. © 1968.