To investigate if granulocyte and monocyte apheresis mitigates the symptoms of rheumatoid arthritis (RA), and influences production of panmyelocytes (CD15+ CD16- cells) at the bone marrow level, 27 RA patients who had elevated granulocyte counts were recruited. The granulocyte and monocyte apheresis column (G-1 column) is an extracorporeal type device packed with 220 g cellulose acetate beads to which granulocytes and monocytes specifically adhere. Patients received apheresis of 1 hr duration twice per week, 8 times over a period of 4 weeks. To prepare CD15+CD16- cells, iliac bone marrow aspirate was obtained at baseline and at 2 weeks after completion of the apheresis course. Ex-vivo proliferation of bone marrow low density cells and production of IgM-RF were also investigated. Following granulocyte and monocyte apheresis, there was a suppressed tendency in the number of CD15+CD16- cells in patients with high bone marrow CD15+CD16- cell counts at baseline. Clinical assessments 2 weeks after the completion of apheresis therapy showed improvements in swollen joint count (P < 0.001), tender joint count (P < 0.001) and duration of morning stiffness (P < 0.005). The results suggest that granulocytes and monocytes/macrophages have a pathological role in RA and apheresis treatment to reduce or suppress these cells should benefit patients with RA.