A 45-year-old female with a long history of HLA-B27-positive ankylosing spondylitis and ulcerative colitis developed cyclic neutropenia. She was hospitalized for high fever during each of three consecutive episodes of absolute neutropenia. On the third hospitalization, granulocyte-colony-stimulating factor (G-CSF), 5 micrograms/kg/day, was given by subcutaneous injection and resulted in an increase of absolute neutrophil count from 0 to 2.2 x 10(9)/liter and an associated decrease of platelet count and hemoglobin as well as severe bone and joint pain predominantly in the middle and lower back and purulent diarrhea. The back pain necessitated discontinuation of the drug. Oral cyclosporine therapy was begun, and although the neutrophil count continued to oscillate, both the peaks and the nadirs were higher than previously, and symptoms of neutropenia subsided. We conclude that cyclosporine can be an effective treatment for cyclic neutropenia associated with autoimmunity since G-CSF may cause exacerbations of autoimmune disorders.