Homogeneous liposome immunoassay for the determination of phenytoin was studied.Liposomes were prepared from cholesterol (CH) and phospholipids including dipalmitoyl phosphatidyl ethanolamine (DPPE) tbr conjugation with thiol-containing antibodies. Hemin chloride was entrapped in the liposome and antibody was modified by reaction with 3’ (2-pyndyl-dithio) propionyl N-hydroxysuccinimide ester (SPDP) to introduce thiol groups for efficient coupling. Antibody-coupled liposomes (immunoliposomes) were incubated with phenytoin and complement, and then with hemin substrate. The amount of hemin released from immunoliposomes, which increases with concentration increase of phenytoin, can be detected rapidly by determining the fluorescence with its substrate p-hydroxyphenyl propionic acid (HPPA)and hydrogen peroxide.