This work establishes the presence of a microbody-like organelle in a unicellular red alga,Porphyridium purpureum (Bory) Drew et Ross. There are several of these per cell. They are spherical or slightly ovoid in shape and 0.2–0.4 microns in diameter. A strongly positive reaction to the diaminobenzidine cytochemical test was noted in this organelle. Inhibition of the DAB reaction with standard reagents gave unusual results. These results suggest that catalase may be absent, the staining in the microbodies being due to peroxidase. Staining was noted in the chloroplast lamellae in neutral conditions in the presence of light. No staining was noted in the mitochondria. To our knowledge this is the first report of a microbody-like structure in a member of theRhodophyceae.