We studied intracellular cytokines in monocytes by flow cytometry from 28 patients with hematologic malignancies and solid tumors to analyze the role of monokines in the hematologic recovery phase for peripheral blood stem cell harvest. The patients were divided into three groups: the first group, A, had a documented infection; the second group, B, had fever of unknown origin; and the third group, C, was afebrile. We found an increase in intracellular IL-1alpha, IL-6, IL-8 and TNF-alpha positive monocytes as CD14 positive gated cells cultured with lipopolysaccharide in all groups, but no increase was found with medium only when cultured for 4 h. We also found an increase in intracellular IL-1a, IL-6, IL-8 and TNF-alpha positive monocytes cultured with autologous serum for 4 h, but only in group A. The rate of intracellular cytokine positive cells was higher in monocytes cultured with only autologous serum from group A patients compared to those cells from the other groups; the data concerning IL-1a, IL-6 and TNF-alpha reached statistical significance (P < 0.05). However, increasing intracellular cytokine levels in the control group of patients exhibiting only infectious disease were observed. Thus, it appear that pro-inflammatory intracellular cytokine levels in monocytes are only related to microbial infections.