In this article two patients are reported with recurrent upper airways and ENT-infections. Laboratory investigation showed a persistent neutropenia. The bone marrow aspirations showed a normal cellularity of the erythroid series and the megakaryocytes. The myeloid series were normal with a decreased number of mature segmented neutrophils. In these patients the serum levels of immunoglobulins were within normal range and antibodies against the white cells could not be demonstrated. By the age of 2-3 years the recurrence of infections had decreased and infections of importance have not been reported since. By that age the peripheral white count was not abnormal. This combination of signs and symptoms is known as 'chronic benign neutropenia'. The etiology is obscure. Our investigation in one case (by that time recovered) showed a diminished growth of the myeloid series of donor bone marrow in the presence of patient's serum. This suggests a plasma-factor responsible for the maturation of the myeloid series. This finding has not yet been reported in the literature.