CD1 molecules are glycoproteins present primarily on dendritic cells (DCs), which recognize and presenta variety of foreign- and self-lipid antigens to T-cells. Humans have five different CD1 isoforms that sur-vey distinct cellular compartments allowing for recognition of a large repertoire of lipids. The canine CD1family consists of seven functional CD1 molecules (canine CD1a2, CD1a6, CD1a8, CD1a9, CD1b, CD1c andCD1e) and one presumed non-functional isoform (canine CD1d) due to a disrupted gene structure. Theaim of this study was to describe in vitro steady-state localization ptterns of canine CD1 isoforms andtheir correlation with endocytic organelles. GFP-fused canine CD1 293T cell transfectants were stainedwith markers for early endocytic compartments (EEA-1) and late endocytic/lysosomal compartments (LAMP-1), respectively, and analyzed by confocal microscopy. Canine CD1a molecules localized to theplasma membrane and partially to the early endocytic compartment, but not to late endosomes or lyso-somes. In contrast, canine CD1b was highly associated with late endosomal/lysosomal compartments andshowed a predominant intracellular expression pattern. Canine CD1c protein expression localized morepromiscuously to both the early endosomal compartments and the late endosomal/lysosomal compart-ments. The canine CD1e molecule showed a strictly intracellular expression with a partial overlap withlate endosomal/lysosomal compartments. Lastly, canine CD1d was expressed abnormally showing onlya diminished GFP expression. In conclusion, canine CD1 transfectants show distinct localization patternsthat are similar to human CD1 proteins with the exception of the canine CD1d isoform, which most likelyis non-functional. These findings imply that canine CD1 localization overall resembles human CD1 traf-ficking patterns. This knowledge is important for the understanding of lipid antigen-receptor immunityin the dog.