OBJECTIVE This study investigated the bacterial and fungal contamination of used dental burs. A novel assay system for comparison of efficacy of pre-sterilisation cleaning techniques for dental burs was used to evaluate manual scrubbing, enzymic agents and washer-disinfectors. METHODS Thirty dental burs contaminated during cavity preparation were analysed for micro-biological total viable counts and species of bacteria and fungi present. To simulate clinically contaminated burs, a culture of Streptococcus sanguis NCTC 7863 was used to inoculate unused dental burs, alone and combined with blood, saliva or a mixture of blood and saliva. Contaminated burs were subjected to six pre-sterilisation cleaning techniques and the log reduction in contamination achieved by each method was assessed. RESULTS The microbial count from used dental burs ranged from 0 to 6.92 x 10(4) CFU ml(-1). Many potentially pathogenic species were identified. The decontamination assay demonstrated that autoclaving alone was not sufficient to sterilise dental burs. Manual scrubbing in air was less efficacious than manual scrubbing under water (p<0.001). The most effective method of pre-sterilisation cleaning for dental burs was a washer-disinfector. CONCLUSIONS Enzymic agents are suitable for soaking contaminated dental burs immediately after use. Washer-disinfectors are recommended as the method of choice for pre-sterilisation cleaning of contaminated dental burs.