OBJECTIVE Recently, the use of ortho-phthalaldehyde (OPA) has been increasing as an alternative to glutaraldehyde for endoscope disinfection. To better understand OPA exposure and its health effects among disinfection workers, we conducted environmental monitoring and administered a questionnaire in 17 endoscope disinfection rooms. There were 9 manual disinfection rooms using immersion vats for scope disinfection and 8 automatic rooms using automatic washers. RESULTS OPA exposure concentration during the disinfection process of scope was significantly higher in the manual group (median: 1.43ppb, range: not detected (ND-5.37ppb) than in the automatic group (median: 0.35 ppb, range: ND-0.69 ppb). Similarly, during charging and discharging the antiseptic solution, OPA levels were significantly higher in the manual group (median: 2.58 ppb, range: 0.92-10.0 ppb) than in the automatic group (median: 0.46ppb, range: ND-1.35 ppb). Time-weighted averages of OPA exposure concentration during work shifts were 0.33 to 1.15 ppb (median 0.66 ppb) in the manual group and 0.13 to 1.28 ppb (median 0.33 ppb) in the automatic group, which suggests that manual workers are exposed to OPA at higher levels. Among 80 female disinfection workers who used only antiseptic solutions containing OPA, the incidence of disinfection-related complaints were 10% skin, 9% eye, and 16% respiratory symptoms. CONCLUSIONS These findings suggest that it is desirable to introduce automatic washers to decrease OPA exposure levels among disinfection workers.