The effect of serial bathing (10-minute bathing in city water or Misasa hot spring, 40℃, once daily for one or four weeks) on the circadian variations of plasma metabolites was studied in three groups of rats : hot spring bathing rats, city water bathing rats and non-treated rats. Plasma obtained by decapitation at 8:00, 12:00, 16:00, 20:00 and 24:00 hours was analysed for catecholamines (CA), free fatty acids (FFA), cholesterol (C) and glucose. 1) Noradrenaline (NA) and adrenaline (A) were significantly lower at 24:00 hours with significantly lower 24-hour average concentrations and also with significantly different diurnal patterns in the 1-week hot spring bathing rats; in the 4-week hot spring bathing rats, lower 24-hour average concentrarion of A was the only significant finding. The results suggest the suppressive effect of hot spring bathing on the sympathetic system or pituitary gland-adrenal medulla; they also suggest the adaptation to hot spring bathing. 2) Free fatty acids were significantly higher in the 1-week hot spring bathing rats at 12:00 hours as compared with non-treated rats and city water bathing rats. The 4-week hot spring bathing rats showed concentration of FFA not different from the remaining two groups of rats. No significant difference was noted in diurnal patterns among the three groups of rats. The results suggest that the high FFA concentrations in the 1-week hot spring bathing rats are related to the physico-chemical constituents of the hot spring to some extent and that the rats adapt
themselves to bathing during the 4-week preriod. 3) Cholesterol was significantly lower in the 4-week hot spring bathing rats as compared with non-treated rats and city water bathing rats; no different diurnal patterns were noted among the three groups of rats. The results suggest the suppressive effect of 4-week hot spring bathing on plasma cholesterol concentrations as reported previously by us. 4) No Significant difference was noted in concentrations as well as in diurnal patterns of plasma glucose among the three groups of rats. The results suggest that bathing has no significan effect on concentrations and diurnal patterns of plasma glucose in healthy rats.