A health evaluation request was received from a state health department asking NIOSH investigators to evaluate the hazard to workers in a mycobacteriology laboratory from an ultraviolet (UV) radiation disinfection system. Of the 76 measurements taken, 16 were near the NIOSH recommended exposure limit, with the highest exposure being about twice the limit. Actions had been taken at the laboratory to reduce UV exposure before the survey. Some of these actions included the painting of ceilings with UV absorbing paint containing titanium-dioxide as the absorbing agent. The fixtures were lowered by 15 to 30 centimeters to increase the path length between the source and the worker, thus reducing the workers' exposures. Other methods for reducing exposure included the use of shielding and personal protective equipment. Disinfecting systems such as this have been encountered also in hospitals, offices, and manufacturing facilities. The author concludes that these methods are effective in controlling aerosolized pathogenic organisms, as was the case in the laboratory examined. Overexposure to UV radiation was noted to cause injuries to the eyes and skin.