OBJECTIVES: To report on the skin discoloration experienced by three workers handling 2 , 5 -hexanedione METHODS: Three workers, who showed orange-brown discoloration of the palms during observation under the Kumi occupational disease surveillance system, had their history evaluated and underwent physical examination. A workplace survey was performed by an occupational physician and an industrial hygienist. RESULTS: The three workers were determined to have been experiencing skin discoloration since the introduction of a new cleaning solvent. The new solvent contained 2,5-hexanedione, which is reported in the literature to be possibly capable of causing orangebrown discoloration of the skin. After discontinuation of solvent use, the workers recovered within a week. CONCLUSIONS: These cases demonstrate that 2,5-hexanedione can produce skin pigmentation.