To estimate canine interleukin-8 (cIL-8) levels in blood plasma samples, a sandwich enzyme linked immunosorbent assay (ELISA) was established. For the development of the sandwich ELISA, polyclonal anti-cIL-8 (capturing), biotinylated anti-cIL-8 (developing) antibodies and glutathione-S-transferase/cIL-8 (GST/cIL-8) fusion protein as an antigen were used. cIL-8 in the fusion protein of GST/cIL-8 was detected in a dose dependent manner. The lowest limit of GST/cIL-8 detectable by this method was 2 ng/ml of GST/cIL-8 (containing; 0.470 ng/ml of cIL-8). IL-8 levels in the plasma samples from apparently healthy dogs were less than 0.470 ng/ ml. Higher levels of IL-8 were detected in the plasma samples of dogs with cystitis, dermatitis, and gastric cancer. These results suggest that the determination of cIL-8 by the sandwich ELISA is useful in diagnosis of inflammatory diseases in dogs.