The discovery of the CD1 antigen-presenting system reveals that T cells survey the lipid content of target cells via T-cell receptor (TCR) contact with CD1 bound to lipids, glycolipids and small molecules. Recently, CD1 proteins have been found to present mycobacterial lipopeptides that are involved in scavenging iron from infected cells. The mechanism of lipopeptide antigen presentation by CD1 involves the anchoring of antigens in the hydrophobic binding groove, resulting in exposure of the peptide moiety for TCR contact. These findings expand the range of known antigens for T cells and raise the intriguing possibility that CD1, similar to MHC class I and II molecules, enables T cells to discriminate among peptide sequences.