Neutralization of endogenous interleukin (IL)-4 or IL-10 in mice with Candida albicans infection initiates or accelerates development of a T helper (Th)1-associated protective response. Here, we report the effect of IL-4 and IL-10 administration on the course of systemic or gastrointestinal (GI) candidiasis and on the development of Th immunity using yeast/host combinations that result either in Th1-associated self-limiting infection (healer mice) or in Th2-associated progressive disease (nonhealer mice). Treatment with IL-4 or IL-10 greatly exacerbated the course of systemic infection in nonhealer mice and rendered healer mice, inoculated with attenuated yeast cells, susceptible to infection. Under the latter conditions of yeast challenge and IL-4/IL-10 administration, the development of a fatal disease was associated with inhibition of IL-12 production and detection of progressive Th2 cell dominance. In contrast, in healer mice allowed to resolve their infections and to develop long-lived anti-candidal resistance, the expression of this acquired resistance was not impaired by IL-4 and/or IL-10, as shown by the outcome of reinfection with virulent yeast cells. In the GI model of infection, both IL-4 and IL-10 were found to exacerbate the course of infection and to induce the appearance of CD4+ T cells producing high levels of IL-4 and IL-10 in Peyer's patches. These findings demonstrate that exogenous IL-4 and IL-10 may greatly affect the development of Th responses to C. albicans in vivo, but do not modify the expression of established and predominant Th1 cell reactivity.