The benefits of adding bovine serum albumin (BSA) or T4 gene 32 protein (gp32) to PCR were evaluated with reaction mixtures containing substances that inhibit amplification. Whereas 10- to 1,000-fold more FeCl3, hemin, fulvic acids, humic acids, tannic acids, or extracts from feces, freshwater, or marine water were accommodated in PCR when either 400 ng of BSA per microl or 150 ng of gp32 per microl was included in the reactions, neither BSA nor gp32 relieved interference significantly when minimum inhibitory levels of bile salts, bilirubin, EDTA, NaCl, sodium dodecyl sulfate, or Triton X-100 were present. Use of BSA and gp32 together offered no more relief of inhibition than either alone at its optimal level, and neither protein had any noticeable effect on amplification in the absence of inhibitors.