CD8 sup + cytotoxic T lymphocytes (CTLs) mediate resistance to infectious agents and tumours.Classically, CTLs recognize antigens that are localized in the cytoplasm of target cells, processed and presented as peptide complexes with class I molecules of the major histocompatibility complex (MHC) . However, there is evidence for an exogenous pathway whereby antigens that are not expected to gain access to the cytoplasm are presented on MHC class I molecules [2-6]. The most dramatic example is the in vivo phenomenon of cross-priming : antigens from donor cells are acquired by bone-marrow-derived host antigen-presenting cells (APCs) and presented on MHC class I molecules. Two unanswered questions concern the identity of this bone-marrow-derived cell and how such antigens are acquired. Here we show that human dendritic cells, but not macrophages, efficiently present antigen derived from apoptotic cells, stimulating class I-restricted CD8 sup + CTLs. Our findings suggest a mechanism by which potent APCs acquire antigens from tumours, transplants, infected cells, or even self-tissue, for stimulation or tolerization of CTLs.