We sought to determine whether measurement of Histoplasma capsulatum var. capsulatum antigen concentration in tissues and blood provided a marker for antifungal effect of itraconazole in a nonlethal murine model of histoplasmosis. Treatment with itraconazole (Sporanox), in cyclodextrin, was evaluated in a pulmonary model of histoplasmosis. Mice infected with 4.0 x 10(7) yeast-phase organisms by endotracheal inoculation were treated with itraconazole, 1.5 mg twice daily by gavage, for 10 consecutive days, beginning on day 4 of infection. All mice were sacrificed on day 15 of infection. Blood, spleen, and lung tissues were removed for culture and quantification of antigen. Numbers of organisms were significantly lower in spleens from the treated group: 20.8 +/- 41.8 vs. 65.8 +/- 39.1 in the control group, P = 0.017. Numbers of organisms in lung were 9.6 +/- 27.3 colony forming units in treated versus 24.2 +/- 36.3 in control animals, P = 0.267. Antigen concentrations in spleen tissue and serum were lower in treated versus control mice: spleen, 1.8 +/- .6 units in treated versus 11.0 +/- 2.3 in controls, P < 0.001; serum, 0.8 +/- 0.2 units in treated versus 2.2 +/- 1.0 units in controls, P < 0.001. Lung antigen concentrations were similar in the two groups, 19.2 +/- 1.4 units in treated compared to 17.9 +/- 3.0 units in control mice, P = 0.142. The cyclodextrin formulation of itraconazole (Sporanox) demonstrated antifungal activity in experimental histoplasmosis. Antigen detection was a useful marker for antifungal effect.