Isopycnic sucrose density gradient centrifugation of cell-free extracts of a yellow mutant of Chlorella vulgaris and its green parent strain showed a distribution of catalase and glycollate oxidoreductase activity consistent with their association with a particle/organelle fraction. Gradient centrifugation starting from a pellet of cell-free material resulted in a concentration of enzyme activity in the 1.5 M to 2.0 M sucrose fractions which coincided with a microbody-containing fraction as determined by electron microscopy. The algal glycollate-oxidizing enzyme coupled to oxygen, oxidized both d- and l-lactate and was insensitive to cyanide in vitro, showing it to be similar to that of higher plants. The association of glycollate oxidase together with catalase, with the microbody fraction, may be taken as evidence for the presence of algal peroxisomes in these organisms.