A rapid polymerase chain reaction (PCR) method to obtain taxa-specific DNA probes has been developed. The oligonucleotide probes derived from the sequences of species-specific (or other taxa) random amplified polymorphic DNA (RAPD) fragments. The methodology was applied to design probes for the halophilic archaeal species Haloferax mediterranei. With this technique, DNA probes of known sequence can be generated easily and without any previous knowledge about the properties of the microorganisms.