Four local hospitals using CIDEX(asterick) Activated Dialdehyde Solution in CIDEMATIC(asterick) Decontamination Machines or otherwise were selected for monitoring glutaraldehyde vapors. Glutaraldehyde levels were monitored in anesthesia and respiratory therapy departments on two occasions: (1) at the time the CIDEX Solu- tion was changed, and (2) at the time the CIDEX Solution had been activated for one week. In almost every department monitored, the level of glutaraldehyde vapor remained at less than or equal to 0.2 ppm, which is below the Human Sensory Irritation Threshold valued defined at Arbrook, Inc. Interviews with hospital personnel using CIDEX Solution gave no indication that CIDEX odors were irritating at the 0.2 ppm level. With proper technique and care, the hospital personnel working with CIDEX Solution can keep the odor level below 0.2 ppm.