The effect of lithium on hematopoietic system makes an interesting, albeit somewhat forgotten topic of research, which started in the 60's and has continued into the 70's and the 80's of the 20th century. The most important actions of lithium concern the increase in the granulocyte count and modulation of their function, the increase in the platelet count, also in patients after chemotherapy and radiotherapy, the decrease in T-lymphocytes, in NK cells activity and in the production of immunoglobulins. The data of lithium effect on erythropoiesis are equivocal. The effect of lithium on blood cells enables its application in the treatment of hematological disorders, particularly congenital and iatrogenic neutropenia. In a murine model of AIDS (MAIDS), lithium improves hematopoiesis and reduces splenomegaly, lymphadenopathy as well as hypergammaglobulinemia. Also, increased tolerance of zidovudine and amelioration of myelosuppression and thrombocytopenia have been noted. Lithium is effective in treating neutropenia induced by clozapine, carbamazepine, cyclophosphamide, vinblastine and radiotherapy. Lithium has a positive effect on the number of leukocytes in patients with lymphosarcoma, prostate cancer, Hodgkin and non-Hodgkin lymphoma and in multiple myeloma. A shorter duration of neutropenia, less severe febrile neutropenia episodes, fewer days of hospitalization with fever and neutropenia, fewer infection-related deaths and improved quality of life were observed in patients with various types of cancers receiving additional lithium therapy. Lack of effect of lithium was observed in neutropenia associated with glycogenosis, during chemotherapy of acute myeloid leukaemia and in leukaemia of T-cell large granular lymphocytes.