The effects of various physiological factors and stress conditions on serum serotonin levels were examined in normal subjects, that is, the relationship of aging, circadian rhythm, ingestion of diet, physical exercise, sleep deprivation and alcohol ingestion to serum serotonin levels were investigated, and the following results were obtained. 1) As to age, serum serotonin levels were significantly higher in children below 10 years of age, and decreased gradually until age 30. 2) Sexual difference of serum serotonin levels was not found. 3) The circadian rhythm of serum serotonin levels were examined at 8,12,20 and 24 o'clock, but a significant rhythm was not observed. 4) The ingestion of a normal diet (960 Cal per meal) did not exert any influence upon serum serotonin levels. 5) Similarly, the ingestion of a high serotonin diet (banana) did not exert any influence. 6) After the load of physical exercise (2 hours of basketball playing), serum serotonin levels showed a slight increase, but it was not statistically significant. 7) Serum serotonin levels were determined during one-night of sleep deprivation, but there was no significant change because of it. 8) The effect of acute alcohol ingestion (oral ingestion of Japanese sake, 540-1800 ml) was determined. As a result, serum serotonin levels showed the tendency to increase 12 hours after ingestion as compared with the level before ingestion. 9) In one patient who had drunk alcohol for 18 years, an abrupt transient increase of serum serotonin level was observed when he stopped drinking. The effects of various physiological factors and stress conditions on serum serotonin levels were examined in normal subjects, that is, the relationship of aging, circadian rhythm, ingestion of diet, physical exercise, sleep deprivation and alcohol ingestion to serum serotonin levels were investigated, and the following results were obtained. 1) As to age, serum serotonin levels were significantly higher in children below 10 years of age, and decreased gradually until age 30. 2) Sexual difference of serum serotonin levels was not found. 3) The circadian rhythm of serum serotonin levels were examined at 8,12,20 and 24 o'clock, but a significant rhythm was not observed. 4) The ingestion of a normal diet (960 Cal per meal) did not exert any influence upon serum serotonin levels. 5) Similarly, the ingestion of a high serotonin diet (banana) did not exert any influence. 6) After the load of physical exercise (2 hours of basketball playing), serum serotonin levels showed a slight increase, but it was not statistically significant. 7) Serum serotonin levels were determined during one-night of sleep deprivation, but there was no significant change because of it. 8) The effect of acute alcohol ingestion (oral ingestion of Japanese sake, 540-1800 ml) was determined. As a result, serum serotonin levels showed the tendency to increase 12 hours after ingestion as compared with the level before ingestion. 9) In one patient who had drunk alcohol for 18 years, an abrupt transient increase of serum serotonin level was observed when he stopped drinking. The effects of various physiological factors and stress conditions on serum serotonin levels were examined in normal subjects, that is, the relationship of aging, circadian rhythm, ingestion of diet, physical exercise, sleep deprivation and alcohol ingestion to serum serotonin levels were investigated, and the following results were obtained. 1) As to age, serum serotonin levels were significantly higher in children below 10 years of age, and decreased gradually until age 30. 2) Sexual difference of serum serotonin levels was not found. 3) The circadian rhythm of serum serotonin levels were examined at 8,12,20 and 24 o'clock, but a significant rhythm was not observed. 4) The ingestion of a normal diet (960 Cal per meal) did not exert any influence upon serum serotonin levels. 5) Similarly, the
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