In the present study, lectin cytochemistry in combination with enzyme and chemical treatments and ultrastructural immunocytochemistry were applied to investigate the formation of acrosomal glycoproteins in endoplasmic reticulum (ER) and Golgi apparatus (GA) of early rat spermatids. In addition, the vesicles involved in glycoprotein traffic were investigated using a monoclonal antibody against clathrin. The results obtained suggest the occurrence of high mannose and complex type N-linked oligosaccharides and mucin type O-linked oligosaccharides. In N-linked glycoproteins, Man residues are incorporated into the nascent oligosaccharide in the ER, Fuc residues of the inner core of the oligosaccharide in the cis region of GA, GlcNAc in medial cisternae of GA and Gal residues in the transmost cisternae of GA. In O-linked glycoproteins, the addition of GalNAc occurs in cis and trans cisternae of GA. Gal beta 1,3GalNAc sequence was detected in medial and trans cisternae of GA. Sialic acid was detected in both N- and O-linked oligosaccharides in medial and trans cisternae of GA but not in acrosomes. Immunoreactivity to clathrin was observed in the intermediate zone between ER and GA and in vesicles of the trans side of GA.