The disposition kinetics of lithium were studied in six elderly women who had been maintained on this medication for several years. Lithium administration was stopped abruptly. Plasma, whole blood, and erythrocyte half-lives were then measured, as well as renal plasma clearance and distribution volume. Half-life values in whole blood and in its components were found to be similar. The plasma lithium half-life approximated that in younger schizophrenics, but appeared prolonged when compared with half-lives reported for young normal volunteers. Renal plasma clearance and distribution volume of lithium appeared substantially reduced when compared with published values. The data are consistent with altered lithium disposition in the aged.