Donor leukocyte infusions (DLI) from the original marrow donor have been shown to induce remission in patients with relapse after BMT. We analyzed factors that were associated with remission. Twenty-six patients with a relapse after T cell depleted BMT received DLI. The following pre-DLI factors were analyzed: sex and age of the patients and donors, GVHD after BMT, indication for DLI, percentage of donor T lymphocytes in the patient at the time of DLI, interval between relapse and DLI, and number of T lymphocytes infused. Remission was achieved in 11 of 15 patients (73%) treated for relapsed CML and in one of 11 patients (9%) treated for relapsed AML, ALL or RAEB-t (P = .002). Two of 13 patients (15%) with < or =40% of T lymphocytes from donor origin attained remission compared with 10 of 13 patients (77%) with >40% (P = .002). Two of 13 patients (15%) with an interval of < or =18 months between BMT and first DLI entered remission compared with 10 of 13 patients (77%) with an interval of >18 months (P = .002). Multivariate analysis demonstrated that indication for DLI (CML versus AML/ALL and RAEB-t) and the percentage T lymphocytes from donor origin (< or =40 versus >40) were significantly correlated with remission (P = .03). The occurrence of GVHD post DLI was highly associated with achievement of remission (P = .0001). DLI res ults in remission in a high percentage of patients with relapsed CML after BMT. The percentage of T lymphocytes from donor origin still present in the patient at the time of DLI is highly correlated with achievement of remission.