Several human monoclonal antibodies directed to tumor-associated glycolipid antigens have been established, but more than one-half of them react with gangliosides and the others react with neutral glycolipids. We report here the first establishment of a human IgM monoclonal antibody directed to the sulfated glycolipid. This monoclonal antibody, M14-376, did not react with SM3 and SB1a which have a terminal HSO3----3Gal beta 1----R1, but with the simple sulfolipids SM4s-Gal and SM4g which contain a terminal HSO3----3Gal beta 1----O----CH2----R2; however, lyso-SM4s-Gal and lyso-SM4g did not bind M14-376. These results suggest that terminal HSO3----3Gal and part of the hydrophobic region of the glycolipid are recognized by M14-376. Directly biotinylated M14-376 was used for immunohistochemical staining of 140 formalin-fixed, paraffin-embedded lung cancer tissue sections to study the distribution of the antigen. A high incidence of positive staining was found in adenocarcinoma (39.5%, 17 of 43), followed by large cell carcinoma (20.0%, 5 of 25), while this antigen was rarely detected in small cell carcinoma (4.7%, 1 of 21) and squamous cell carcinoma (3.9%, 2 of 51). Thin layer chromatography immunostaining of glycolipids extracted from lung cancer tissues showed the presence of only SM4s-Gal in adenocarcinoma, but SM4g was not found in any subtype of lung cancer. Immunohistochemical staining revealed that this antigen was expressed in normal kidney, testis, and brain, but erythrocytes, granulocytes, and lymphocytes were negative in cytofluorometric analysis.