Methods for identifying isolates of various pathogenic bacteria by DNA fingerprinting with random primers (RAPD) have been described recently. In these methods many primers are screened and the primers that generate the most informative DNA pattern are selected. A new strategy that simplifies the primer selection process for RAPD fingerprinting has been developed in our laboratory. In this approach, one or more degenerate nucleotides is introduced into the core RAPD primer sequence at various nucleotide positions. Results show that a single degenerate nucleotide in the primer sequence can significantly change the DNA profile obtained for the same template. The more removed the degenerate nucleotide is from the 3' end of the primer, the less dramatic is its effect on banding pattern. This method utilizing degenerate RAPD (D-RAPD) primers was tested on clinical isolates of Legionella pneumoniae, and results were confirmed with nondegenerate RAPD primers. Results obtained with D-RAPD primers were in total agreement with those obtained with nondegenerate RAPD primers. We propose that the use of a core RAPD primer sequence with one or more degenerate nucleotide(s) at various positions can expedite the generation of unique DNA fingerprints individual organisms. A general method for selecting the most useful fingerprinting RAPD primers is discussed.