We studied the production of cytokines by peripheral blood monocytes and T cells during the period of haematological recovery following intensive chemotherapy. Twelve adults with haematological malignancies received consolidation chemotherapy of complete remission. Monocytes and T cells were collected during the phase of recovery from intensive chemotherapy, and were incubated for 24 h in a culture medium with 10% FCS. Concentrations of cytokines in the culture supernatant were measured with an enzyme-linked immunosorbent assay. During the recovery phase, concentrations of IL-6, G-CSF and IL-1 beta in the culture supernatant of the collected monocytes significantly exceeded those of the monocytes obtained from normal healthy subjects. Similarly, the concentrations of GM-CSF and IFN-gamma in the supernatant of recovery phase T cells significantly exceeded those of normal T cells. Plasma levels of these cytokines were also elevated. These data suggest that the monocytes and T cells may be activated in vivo to produce haemopoietic cytokines during haematological recovery, and that, during haematological recovery, the monocytes and T cells may be actively involved in the induction of haematopoiesis following the myelosuppression induced by chemotherapy.