Severe neutropenia is a common feature in patients with T-large granular lymphocytic (LGL) leukemia. Neutropenia often causes severe infections and septicemia, thus representing a major cause of morbidity and mortality in this disease. We have treated two outpatients with T-LGL leukemia who had severe neutropenia (neutrophils < 0.2 x 10(9)/l) successfully with G-CSF (5 micrograms/kg daily, s.c.). After 10 days of treatment the neutrophil count was within the normal range and a severe oral infection healed rapidly. We conclude that G-CSF therapy is able to normalize the neutrophil count in T-LGL leukemia within a few days and that it can be used to treat severe infections in these patients even on an outpatient basis.