Macrophages are essential for the proliferative response of human T lymphocytes to a purified polysaccharide extract from Candida albicans (MPPS). The role of macrophages as antigen-presenting cells in the production of an antigen non-specific inhibitory factor (nsINH) by MPPS-activated T cells was also investigated. Fc receptor positive (FcR+) or negative (FcR-) plastic-adherent mononuclear cells were used as MPPS-presenting cells, and the results show that the FcR- subset is mainly responsible for the release of nsINH from activated T cells.