Randomly amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) was performed on DNA templates prepared from thirty veterinary Salmonella typhimurium isolates. The templates were isolated by four different methods, each differing in their level of purity as determined by 260 nm/280 nm ratios. Dendrogram analysis of RAPD-PCR amplification patterns resulted in the organisms being placed into a range of 26-12 discrete groupings dependent on the DNA template isolation method used. Thus, DNA purity plays an important role in amplification patterns obtained by RAPD-PCR and investigators must consider this variable before making judgements on the genetic relatedness of a group of organisms.