A variety of sialic acids contained in the rat epididymis were histochemically examined by means of lectin and pre-lectin methods by light microscopy. Epididymides from adult male Sprague-Dawley rats were fixed in Bouin's fluid and routinely embedded in paraffin wax. Hydrated sections were subjected either to the lectin methods using biotinylated Limax flavus, Sambucus nigra, Sambucus sieboldiana or Maackia amurensis lectins or to the selective periodate oxidation-phenylhydrazine-thiocarbohydrazide-silver protein-physical development technique with or without saponification. The present results revealed that principal cells in the initial segment and caput contain sialic acid linked to alpha2,6-galactose/N-acetylgalactosamine, whereas those in the corpus and cauda include the sialic acid alpha2,3-galactose sequence. Narrow and clear cells involve all the types of sialic acids examined. Basal and halo cells mainly contain sialic acid alpha2,3-galactose. 8- And/or 9-O-acetylated sialic acids were predominantly distributed in principal cells of the initial segment and proximal caput. These findings are taken to indicate that various sialic acids in the epididymis could participate in different physiological functions characteristic of the regions in this organ.