Recent studies suggest that the impairment of circadian clock function causes various pathological conditions, such as obesity, diabetes, and alcoholism, and an altered mRNA expression of clock genes was found under these conditions. However, it remains to be determined whether clock gene expression varies depending on metabolic conditions even in healthy people. To address this issue, we investigated the associations of metabolic parameters and alcohol consumption with mRNA expression of clock genes (CLOCK, BMAL1, PER1, PER2, and PER3) in peripheral blood cells obtained from 29 healthy non-obese elderly men (age 51-78 yrs) who adhered to a regular sleep-wake routine, through a single time-of-day venous blood sampling at approximately 09:00 h. There were significant correlations between (1) waist circumference and mRNA level of PER1 (r =-0.43), (2) plasma glucose concentration and PER2 (r =-0.50), (3) ethanol consumption and BMAL1 (r =-0.43), and (4) serum gamma-GTP concentration (a sensitive marker of alcohol consumption) and PER2 (r =-0.40). These results suggest mRNA expression of clock genes is associated with obesity, glucose tolerance, and ethanol consumption even in healthy people.