We detected sweet potato viruses by NCM-ELISA in the tropics of South and Central America and Southeast Asia. Sweet potato feathery mottle virus was detected in Peru, Mexico, Dominican Republic, Indonesia, and Philippines. The C 2 virus which shows a serological relationship to the sweet potato symptomless virus was detected in Peru, Indonesia, and Philippines. Sweet potato mild mottle virus was detected in Indonesia. An unidentified isometric and aphid-transmitted virus which had been called C-4 was detected in Peru. Sweet potato leaves infected with the C-4 virus showed small whitish spots. Ipomoea setosa showed leaf curl, dwarf, and necrotic spots, and was a suitable diagnostic plant for C-4 by graft inoculation. Macrosiphum euphorbiae transmitted the C 4 in a persistent manner. C 4 was designated as sweet potato leaf speckling virus, tentatively.