It is demonstrated that a diagnostic PCR for Borrelia burgdorferi can be inhibited in the presence of more than 500 ng of host (monkey skin) DNA. The Inhibitor is the host DNA itself. An acceptable value for analytical sensitivitg can be obtained by diluting the skin-B. burgdorferi proteinase K lysate to a level below the inhibitory concentration of the host DNA. Dilution of the lysate may obviate the need for further DNA purification.