Mouse alpha-1-fetoprotein (AFP) is isolated from amniotic fluid. The main preparative stages are purification by immunoadsorbent columns and preparative electrophoresis. Immune sera are prepared by immunization of rabbits followed by isolation of specific antibody molecules and covalent labeling with horseradish peroxidase (HRP). Affinity chromatography purified conjugates are used for immunohistological staining of AFP in embryonic mouse liver. Several fixation schedules are tried. Best results are obtained when fixation is carried out in ethanol-acetic acid mixture.