Twelve children with juvenile chronic myeloid leukemia (JCML) received chemotherapy or bone marrow transplants. The median survival of the patients treated with myelosuppressive agents was 19 months. These results demonstrate that intensive chemotherapeutic and supportive measures can prolong survival in JCML but do not affect ultimate outcome. Purported differentiation inducers--low dose ara-C and 13-cis-retinoic acid--were not effective in two patients. Two patients were prepared for bone marrow transplantation with standard antileukemic cytoreduction regimens; one died very early post-transplant, and the other had early reemergence of his disease. The third transplant patient underwent transplantation after his disease had entered an accelerated phase. He received a different immunosuppressive pretransplant regimen, but the leukemia recurred. The latter two patients initially engrafted with mismatched T cell-depleted marrow grafts, but had recurrence of the disease. Our data suggest that marrow transplantation is possible for JCML patients without HLA-identical donors, but for successful marrow transplantation different measures are necessary to eradicate the abnormal stem cell compartment.