Notch1 is indispensable for T cell development. It is anticipated that Notch1 and other Notch receptors expressed on the surface of thymic T cell precursors are activated by ligands present on environmental cells, including antigen presenting cells (APCs), and involved in positive and negative selections. Notch receptors on peripheral T cells may also be activated by ligands on APCs. Here, we examined the expression pattern of three Notch ligands, Jagged1, 2 and Delta1 in APCs by an immunofluorescence cell staining method and a reverse transcriptase-polymerase chain reaction (RT-PCR) method. Peritoneal macrophages were strongly positive for Jagged1 staining. In contrast, macrophages separated from spleen and dendritic cells (DCs) separated from spleen and thymus showed positive staining for all the three ligands at a similar intensity. An analysis by RT-PCR revealed that peritoneal and splenic macrophages and splenic and thymic DCs, show a distinct pattern in Notch ligand expression. These findings may represent that expression of various Notch ligands in APCs has a physiological relevance in each organ.