1. There were 3,014 cases admitted to treatment with chlorpromazine in doses of 200 to 400 mgm. daily during an 18-month period beginning January, 1955.2. Response to treatment was best in agitated states of most mental disease categories. It was poorest in akinetic states with a good proportion showing a deepening of their depression. Side-effects were infrequent and not serious, appearing in the first 2 weeks and often subsiding on continued therapy. There were no permanent sequelae even after more than 18 months of medication.3. Jaundice occurred in 13 patients, an incidence of 43%. No relation was found between the jaundice and amount or duration of dosage.4. Leukopenia below 2,000 white blood cells cu. mm. was found in 3 patients (.11%) all of whom recovered on withdrawal of treatment.5. Serial tests for total serum bilirubin, serum alkaline phosphatase plus complete blood cell counts were done on 1,215 cases. These periodic checks may have helped in maintaining a low incidence of toxic complications by sustaining clinical alertness.6. During chlorpromazine therapy, the serum alkaline phosphatase rose more frequently than did the total serum bilirubin. Only one-fifth of the cases with alkaline phosphatase values over 8 units were jaundiced, a weak positive correlation.7. Serial serum bilirubin and leukocyte counts during the first 4 months are useful in detecting the onset of toxic jaundice and/or leukopenia.