Swelling followed by erythematopurpuric lesions on sun-exposed areas of the body developed in five patients. All patients were found to have ingested chlorella. The histopathologic changes consisted of swelling of endothelial cells and thrombosis of small blood vessels in the dermis and the subcutaneous fatty tissue. The photosensitizing agent contained in chlorella tablets was proved to be pheophorbide -a and its ester.