Plasma tryptophan concentration in depressive illness and mania.
Total and free plasma trytophan levels were measured in depressive and manic patients before and after recovery. No change was found in total or free plasma trytophan concentration on recovery from depressive illness. Free plasma tryptophan levels were higher in recovered manics than in active manics, and a group of four manic patients tested before and after recovery showed a significant increase in free plasma tryptophan concentration on recovery.