Homogeneous fluorescence polarization immunoassay (FPIA) was applied to the development of an immunoassay of prostaglandin E1 (PGE1) selected as a model of eicosanoids. PGE1 was derivatized with fluoresceinthiocarbamyl ethylenediamine and purified by thin layer chromatography (TLC). The purity was checked by high performance liquid chromatography (HPLC). A radioimmunoassay was realized to ensure of the immunocompetition of the tracer. After the determination of the concentration of antiserum by fluorescence polarization, the feasability of the immunoassay was shown.