The DNA technology employed in the construction and purification of recombinant antigens has the potential of creating epitopes with specificities other than those of native antigens. Such a phenomenon has been observed when guinea pigs were immunized with Treponema pallidum recombinant antigens, TmpA and TmpB, expressed in Escherichia coli K12. Adsorption of the immune sera with E. coli K12 and T. pallidum revealed the presence of antibodies directed against epitopes not present or exposed in the native antigens of the organisms from which the DNA has been cloned.