Pathomorphological study of trephinobiopsy specimens from 129 patients with lymphoproliferative and myeloproliferative diseases was carried out over the course of chemotherapy. Combinations of initial and manifest myelofibrosis (loose network of reticulin fibers and extensive network of reticulin and collagen fibers, respectively) predominated at the debut of chronic myeloid leukemia, chronic lymphoid leukemia, and multiple myeloma. Manifest myelofibrosis was detected in patients with chronic myeloid leukemia without hematological response (failure of normalization of hematological values) and in patients with progressing and relapsing multiple myeloma. Combinations of foci of initial and manifest myelofibrosis were most incident in patients with progressing and relapsing chronic lymphoid leukemia. The incidence of myelofibrosis was higher in patients with multiple myeloma and chronic lymphoid leukemia progression and relapses and in patients with chronic myeloid leukemia without hematological response than at the disease debut and in case of response to chemotherapy. The response to chemotherapy in patients with chronic myeloid leukemia and chronic lymphoid leukemia was associated with a decrease in the incidence of myelofibrosis. In patients with multiple myeloma responding to chemotherapy, the incidence of myelofibrosis did not change in comparison with the disease debut.