The results of the present investigation, dealing with the rhythmic diurnal and nocturnal changes in blood chemistry and water balance, indicate that the quality of these changes may be correlated with the clinical observation of increased susceptibility to seizures during sleep, particularly after midnight.From the literature may be gained evidence for a shift of the blood and urinary titre toward the alkaline side during the early morning hours, as well as rising intracranial pressure and brain volume during sleep. In addition, the cholesterol content of the blood has been shown to fall consistently during sleep, reaching minimal values at 3 a. m. Each of these changes has been considered by others to be definitely related to the precipitation of seizures in susceptible individuals.The acid-base, water-shifting, and ionic blood changes of the present experiments are qualitatively of the type to encourage the development of seizures during the latter half of the period of sleep. These rhythmic changes are observed to occur in the normal as well as in the epileptic subjects, and may be interpreted as the normal rhythm for blood chemistry.Abstract Teaser