A strain of Salmonella of serotype Salinatis, that produced a mannose-resistant and eluting haemagglutinin (MREHA) when cultured at 37°C but not at 18°C, was examined by electron microscopy after negative staining. Production of this MREHA, previously described as being nonfimbrial, was correlated with the presence of thin fimbriae which had an external diameter of 3.6 nm. The purified Salinatis thin fimbriae had an estimated M r of 19 kDa. This fimbrial MREHA was not produced by strains of the antigenically related serotypes Duisburg and Sandiego.