The author reports on the responses to lithium cabonate of 75 manic-depressive patients. Lithium carbonate was found to be highly effective in the acute manic state but without merit in the treatment of acute depression. Its efficacy was inversely related to age. Response to the drug varied in some patients; a positive response at one time was no guarantee for a similar response in subsequent trials. The possibility of different biochemical states underlying similar clinical states is discussed.Abstract Teaser