Twenty-seven isolates of Burholderia pseudomallei (formerly Pseudomonas pseudomallei) from ten patients with recurrent melioidosis were analysed by RAPD. In two cases RAPD patterns in recurrent isolates differed from the original isolates; one was considered a likely reinfection while the other may represent relapse from one of two strains initially infecting the patient. In two cases where a change in antibiotic resistance had occurred between original and relapse isolates, slight changes in RAPD patterns were found with one of the four primers used. In the other six cases the relapse was clearly due to the original strain re-emerging unchanged, with identical RAPD patterns with all four primers.