For spectrophotometric liposome immunoassay of a specific antibody, antigen (cytochrome c)-coupled liposomes containing the substrate glucose-6-phospbate (G6P) as a marker were prepared from 1,2-di(3RS,7R,11R-phytanyl)-sn-glycero-3-phosphocholine (DPhyPC). DPhyPC liposomes showed good stability against G6P leakage, which was below 8% after incubation for 70 d at 4 degrees C, When cytochrome c-coupled Liposomes were incubated with anti-cytochrome c antibody and complement, after which glucose-6-phosphate dehydrogenase and NAD(+) were added, the absorbance at 340 nm increased with the amount of anti-cytochrome c antibody added.