Granulocyte and platelet recovery as well as platelet transfusion requirements following allogeneic marrow transplantation were analyzed in 67 patients with chronic myelogenous leukemia in the chronic phase. Twenty patients had splenectomy prior to transplantation. Forty-seven patients were transplanted without splenectomy, 21 of whom had splenic enlargement by physical examination. There were no differences in the proportion of patients with granulocyte recovery, but the recovery of peripheral granulocytes to levels of 200, 500 and 1,000/mm3 occurred more rapidly in the splenectomy group than in the no-splenectomy group. Patients with splenectomy received platelet transfusions for a mean of 10 (2-36) days as compared to 20 (3-82) days for patients without splenectomy (p less than .001). Eighteen (90%) patients with splenectomy became platelet transfusion independent at a median of 16 (2-32) days after transplantation as compared to 40 (85%) patients without splenectomy who became transfusion independent at a median of 28 (15-86) days (p less than .001). The proportion of patients achieving platelet levels of 50 and 100 X 10(3)/mm3 did not differ between the two groups (p = .07), but patients in the splenectomy group achieved these levels more rapidly following transplant (p less than .001). One of 17 evaluable patients in the splenectomy group and 31 of 46 in the no-splenectomy group became refractory to random platelets (p less than .001) and required platelets from family members or unrelated completely or partially HLA matched donors. In the no-splenectomy group, splenic size did not affect the speed of granulocyte or platelet recovery or platelet transfusion requirements.(ABSTRACT TRUNCATED AT 250 WORDS)