A 48-year-old woman was admitted in September 1987, because of lumbago and galactorrhea. Peripheral blood analysis showed neutrophilia and eosinophilia without abnormal lymphocytes. The antibody to adult T-cell leukemia (ATL) virus-associated antigen was detected and a hyperprolactinemia was observed. The blastogenic responses to PHA, ConA and PWM were lowered. Brain CT and MRI scannings showed no abnormalities in the hypophysis and hypothalamus, but abdomen CT revealed markedly enlarged abdominal lymph nodes. Two months after the administration of OK432 and PSK, the lymph node swellings disappeared and the responses to PHA, ConA and PWM were normalized, but hyperprolactinemia and galactorrhea persisted. After four months of the remission period, the patient developed lymph node swellings again, and was diagnosed from the biopsy specimen of the retroperitoneal lymph node as having malignant lymphoma of diffuse mixed cell type. Southern blot analysis showed a monoclonal integration of HTLV-I proviral DNA. Despite repeated combination chemotherapies, she died of pneumonia in February 1989. Autopsy revealed marked infiltrations of lymphoma cells in the liver, spleen and lungs, but no abnormality accounting for hyperprolactinemia was detected in the suprasellar regions. This case was of interest in that immunotherapy was effective in achieving a remission and in normalizing immuno-parameters in ATLL.