Plasma imipramine determinations were done in 29 newly hospitalized patients with psychotic depression and in nine normal controls after single oral administrations of 100 mg. of the drug. Two types of curves were found which differed significantly at seven and 24 hours after drug administration.Patients with low oral curves (type A) also had significantly lower plasma imipramine at two hours after intramuscular administration than patients with high oral curves (type B) had. All patients with psychotic involutional depression, as well as normal controls (with one exception), exhibited type A curve. Patients evidencing depressions with manic-depressive psychoses had mainly type B curves.The results are discussed from the point of view of drug binding and metabolism differing according to the functional condition of the central nervous system in the depressions.Abstract Teaser