Abstract:We present here two cases of reversible hypoproteinemia which could have occurred as an adverse effect of chronic lithium administration. In the present cases, protein losing a renal dysfunction, liver dysfunction and malabsorption syndrome were not observed, and the relationship between their dietary volume and serum protein levels was poor. The mechanism of hypoproteinemia in these cases was not identified from previously obtained data. We suggested that this type of hypoproteinemia might be a new adverse effect of lithium