We investigated the effect of nitric oxide (NO) and reactive nitrogen intermediates on the in vitro growth of Penicillium marneffei both in a cell-free system and in a novel macrophage culture system. In the cell-free system, NO that was chemically generated from NaNO2 in acid media (pH 4 and 5) markedly inhibited the growth of P. marneffei. On the contrary, inhibition of growth did not occur in neutral medium (pH 7.4) in which NO was not produced. P. marneffei conidia were phagocytized by nonstimulated murine J774 macrophages after 2 h of incubation. During the following 24 h, P. marneffei grew as yeast-like cells replicating by fission in the J774 macrophages. The intracellular growth of P. marneffei damaged nonstimulated J774 macrophages, as confirmed by electron microscopy. When J774 cells were stimulated by gamma interferon and lipopolysaccharide, which led to enhanced production of reactive nitrogen intermediates, the percentage of yeast-like cells was significantly reduced and P. marneffei conidia were damaged in the J774 macrophages. The inhibition of NO synthesis by N-monomethyl-L-arginine restored the intracellular growth of P. marneffei. The inverse correlation between intramacrophage growth and the amount of nitrite detected in culture supernatants supports the hypothesis that the L-arginine-dependent NO pathway plays an important role in the murine macrophage immune response against P. marneffei.