MANY enveloped viruses contain carbohydrates as components of glycoproteins1–5 or glycolipid6. We have found (unpublished results) that the envelope of Semliki Forest virus (SFV), a group A arbovirus, contains a glycoprotein in which the principal sugars are mannose, galactose and N-acetylglucos-amine and also a glucose-containing glycolipid. It was therefore possible that the virus would react with concanavalin A, the phytohaemagglutinin from jackbean, which specifically binds sugar residues with the α-D-mannopyranoside, α-D-glucopyranoside and α-D-glucosaminyl residues, at branched or terminal non-reducing ends of polysaccharides7.