The POMS (Profile of Mood States) was translated into Japanese, and reliability and validity of the Japanese edition was assessed on 354 healthy males aged 20 to 59 years (mean 42). The following findings were obtained. 1) Reliability coefficients (Cronbach's alpha) were 0.779-0.926 for six mood scales measured by the Japanese edition, i.e. "Depression-Dejection", "Vigor", "Anger-Hostility", "Fatigue", "Tension-Anxiety" and "Confusion." 2) Five factors were extracted by factor analysis for the 65 items of the POMS. "Vigor" and "Anger-Hostility" were solely explained by their respective factors, indicating that these two scales had the highest factorial validity. "Fatigue" had the second highest factorial validity; and "Tension-Anxiety" was third. "Confusion" and "Depression-Dejection" were related to the same one factor. 3) In 33 of the subjects, the scores for mood measured by the POMS were significantly correlated to ratings by a psychiatrist, indicating that the POMS had good criterion-related validity, except for "Anger-Hostility".