In an 18-hospital collaborative study, 255 newly admitted manic patients were randomly assigned to lithium carbonate or chlorpromazine for a three-week period. Patients were classified as highly active or mildly active on the basis of degree of motor activity shown at admission. Treatments were compared in terms of early terminations, symptom change, and toxicity. The following results were obtained: (1) Chlorpromazine was clearly superior to lithium carbonate in treating the highly active patient. Chlorpromazine acted more quickly, produced significantly fewer dropouts, and had a lower incidence of severe side effects. (2) The difference between lithium carbonate and chlorpromazine was less pronounced among mildly active patients. Lithium carbonate, however, appeared to be the better treatment. Both drugs effectively reduced manic symptomatology but lithium carbonate left the patient feeling less sluggish and fatigued. Lithium carbonate also produced fewer severe side effects than chlorpromazine.