Borrelia burgdorferi and Borrelia hermsii were treated with the following detergents: sodium dodecyl sulphate (SDS), N-lauryl sarcosine (Sarkosyl) and Triton X-100, and the soluble and insoluble fractions obtained after each detergent treatment were examined by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Sarkosyl as well as SDS solubilized all Borrelia proteins, whereas Triton X-100 treatment selectively solubilized the majority of other borrelial proteins, leaving two proteins of 41 kDa and 66 kDa in Borrelia burgdorferi and one protein of 39 kDa in Borrelia hermsii associated with the Triton X-100 insoluble fraction.