The polymerase chain reaction (PCR) DNA amplification method is a powerful new tool for the retrospective analysis of paraffin-embedded tissue (PET). The technique has afforded the sensitive and specific detection of nucleic acid sequences associated with genetic and infectious diseases. However, PET processing conditions vary in their suitability for amplification. The authors have examined the effects of 11 fixatives at three fixation times. The effect of fixation was measured by the ability of the DNA in a treated tissue to serve as a template for the amplification of DNA fragments that ranged from 110 to 1,327 base pairs in length. Specimens fixed in acetone or 10% buffered neutral formalin were found to be best suited for subsequent analysis by PCR. A second group of fixatives, including Zamboni's, Clarke's, paraformaldehyde, formalin-alcohol-acetic acid, and methacarn, compromised amplification efficiency. Tissues treated with Carnoy's, Zenker's, or Bouin's, respectively, were even less desirable for amplification analysis.