Histamine and putrescine (a precursor of polyamines) are formed by histidine decarboxylase (HDC) and ornithine decarboxylase (ODC), respectively. Within a few hours after injection of a lipopolysaccharide (LPS) into mice, HDC is induced in the liver, spleen, lung and bone marrow, and ODC is induced in the liver, spleen and bone marrow. Since LPS is known to stimulate the production of various cytokines, the abilities of various cytokines to induce HDC and ODC in the tissues of mice were examined. IL-2, IL-6, IL-8, IFN gamma and M-CSF were ineffective. IL-1 alpha, IL-1 beta, TNF alpha and TNF beta induced HDC and ODC, as does LPS. On the other hand, GM-CSF and G-CSF induced HDC and ODC only in the spleen and bone marrow within a few hours after their injection. These results suggest that, in addition to their roles in inflammation or immune responses, HDC and ODC are also involved in an early stage of hematopoiesis.