Hypogammaglobulinemia in a 22-year-old woman with brief psychotic disorder developed during antipsychotic therapy. Severe decreases in immunoglobulin IgM, IgG, and IgA concentration in serum were observed 4 months after the treatment with chlorpromazine (CPZ) and the other types of antipsychotics. Neither physical diseases nor family history for immunological disturbances was seen. No clinical symptoms in relation to immunological disturbances (i.e. infectious disease), were noted. Gammaglobulin levels in serum returned to a normal range after a replacement of chlorpromazine to timiperone. The hypogammaglobulinemia in the present case was considered to be due to the inhibition of gammaglobulin synthesis by CPZ.