Abstract. In order to set up a disinfection protocol, the tip of the optical fibre of an Nd-YAP laser, =1.34m, was contaminated in vitro with: Mycobacterium smegmatis (CIP 7326), Candida albicans (ATCC 2091), Bacillus stearothermophilus (ATCC 7953) or Streptococcus sanguis (ATCC 10556). It was then treated with various biocidal solutions, Septinol V, glutaraldehyde 2%, ethanol 95 and NaOCl 6%, using one of two protocols: 10s of contact, or 5s of contact followed by 5s of wiping. The latter technique proved to be the most effective. Whatever the biocidal solution used, all the bacteria adhering to the fibre were eliminated. The protocol was checked in vivo in the canals of 10 teeth presenting root canal infections. No bacteria withstood the treatment with Septinol V. This treatment does not alter the qualities and performance of the fibre as far as light transmission is concerned.