The distribution of lithium, sodium and magnesium in rat brain and plasma after various periods of administration of lithium in the diet.

1 The tissue solubilizer Soluene-100 provides an efficient and easy means of preparing small amounts of rat tissue for cation analysis. 2 Administration of lithium ions to rats for two days to 42 days by the addition of lithium chloride to the diet at a concentration of 30 mmol/kg dry weight results in (a) the uniform distribution of lithium throughout the brain at a concentration comparable to that found in plasma; (b) decrease in the brain sodium concentration: (c) a decrease in brain magnesium concentration and an increase in plasma magnesium concentration; (d)no change in brain water content. 3 The inclusion of LiCl in the diet at a concentration of 30 mmol/kg dry food gives consistent and predictable plasma and brain levels of lithium in the rat without the occurrence of serious side effects over periods of up to 42 days.