Through an assessment of affectivity by means of the Crabtree - Horsham Affective Trait Scale, the author was able to predict, with 83-90% accuracy, who would and who would not be judged to be lithium responsive in a sample of hospitalized young adult psychotic patients who received a trial of lithium carbonate. The scale combines an assessment of the psychosis, premorbid personality, family pedigree, family interactional character and the presence or absence of a history of minimal brain dysfunction and drug-induced hypomania. Treatment outcome was found to be significantly better in the group of high affect psychotic patients who received a trial of lithium, when compared with the comparison group of high affect psychotic patients who did not.