Abstract 6-Oxoestriol-6-(0-carboxymethyl) oxime-aminobutylethyl-isoluminol conjugate was synthesized. This luminogenic estriol derivative enabled us to develop a solid phase immunoassay method for the determination of unconjugated estriol in serum of pregnant women by the measurement of the bound estriol-isoluminol conjugate upon oxidation with a hydrogen peroxide/microperoxidase system. The sensitivity of the assay was 700 pmol/1. ...