The structure and the histochemical characteristics of the epidermis of the marine catfish Plotosus lineatus were determined with a series of recent techniques employed either alone or in combination with other procedures to detect selectively sialic acid containing glycoproteins or other acidic carbohydrates. The epidermis consists of a multilayered epithelium where are recognizable various cell types namely, the epithelial cells, the club cells and the mucous or goblet cells the latter concentrated mainly in the outermost layer. The goblet cells and the epithelial cells in the outer epidermis produced both neutral and acidic glycoproteins. The epithelial cells store also acidic glycoproteins containing high amounts of sulphate esters (sulphomucins). The absence of the sialic acid is also discussed.