This study evaluates whether immunohistochemical staining using antibody TKH-2 is presented as a sensitive method for the histological diagnosis of amniotic fluid embolism (AFE). TKH-2 is the sensitive antibody clearly directed to sialyl Tn, NeuAc alpha 2-6GalNAc and reacts with meconium- and amniotic fluid-derived mucin-type glycoprotein. Formalin-fixed, paraffin-embedded maternal lung tissue sections were obtained from four cases of patients showing AFE, and four women uninvolved with AFE served as control. Specimens were stained using the streptavidin-biotin-immunoperoxidase method. The results of immunostaining were compared with those of hematoxylin-eosin (H&E) or a conventional Alcian blue stain. Remarkable positive TKH-2 stainings were observed easily within the pulmonary vasculature in patients with AFE syndrome. AFE can be easily missed on H&E sections. Compared with TKH-2 staining, Alcian blue staining also may be insufficient to show intravascular mucin in the maternal lung sections. TKH-2 immunostaining is the sensitive method to detect meconium- and amniotic fluid-derived mucin in the lung sections of patients with AFE syndrome.