One hundred endoscopes used for bronchoscopy (30), gastroscopy (35) or colonoscopy (35) were studied to determine the efficiency of a new high level disinfectant, orthophthalaldehyde (OPA). Manual cleaning was the method studied since this would be the least effective and thereby provide the greatest challenge to the 0.5% (w/v) OPA solution. The OPA was convenient and easy to use since it did not have irritating vapours and as it is used directly, does not require dilution. Our study demonstrated that the OPA was stable for up to 14 days despite repeated re-use. The cleaning/disinfection procedure could achieve a > or = 5 LOG10 reduction in bacterial load. This in-hospital evaluation supports the conclusion that OPA is an effective choice as a high level disinfectant for flexible endoscopes.