The qualitative nature and distribution of glycoproteins in the mouse epididymis during postnatal development was examined by using lectin cytochemical procedures on paraffin sections and lectin blots on electrophoretically separated luminal fluid polypeptides transferred onto nitrocellulose. Histochemical results revealed the presence of glycoproteins with terminal alpha-D-mannose, N-acetyl-D-glucosamine and neuraminic acid in the principal cells along the epididymis during early stages of development (1st week), and glycoproteins containing terminal alpha-L-fucose, N-acetyl-D-galactosamine and alpha-D-galactose in specific regions of the duct during the differentiation state (2nd-3rd week). Lectin staining localized in the Golgi region and at the apical surface increased during development. Specific changes occurred with age and between cell types. Examination of the epididymal luminal fluid glycopeptides by lectin blot analysis revealed the presence of a large number of glycoproteins with various saccharide moieties at 7 days of age. Epididymal differentiation was accompanied either by the disappearance of some glycoproteins (apparent molecular mass: 16, 17.5, 22, 28, 30 and 74 kDa) or the appearance of new glycoproteins in the proximal (23, 13 kDa) and distal regions (29, 20.5, 19 and 14.4 kDa), or along the entire epididymal duct (26 kDa). The main changes occurred in the epididymis of 21-day-old mice and were completed before spermatozoa reached the epididymal lumen.