The sedation threshold is a determination of the amount of intravenous sodium amytal required to produce certain EEG and speech changes. This paper presents data showing the relationship between the threshold and psychiatric diagnosis in 750 consecutively tested patients. There were also 45 nonpatient control subjects. A large number of statistically significant differences between the thresholds of various diagnostic groups was demonstrated. These differences suggested the use of the threshold for several diagnostic problems, which included: a. measuring degree of manifest anxiety; b. differentiating between hysterical and obsessional personality trends; c. confirming presence of organic psychosis; d. differentiating acute from chronic schizophrenia; e. differentiating neurotic from psychotic depression; f. predicting therapeutic outcome with ECT. It was emphasized that, for clinical purposes, the threshold should be applied within the context of the total clinical picture.