Acetic acid is used in plastics, chemical and pharmaceutical industries. Despite a widespread use, information of possible health effects is sparse. The aim of this study was to evaluate acute irritation during controlled exposure to vapours of acetic acid. Six female and six male healthy volunteers were exposed to 0 ppm (control exposure), 5 and 10 ppm acetic acid vapour for 2 h at rest in a balanced order. Subjective ratings of nasal irritation and smell increased significantly with exposure level. Except for smell, all average ratings at 10 ppm were at the lower end of the 0-100mm visual analogue scale, and did not exceed the verbal expression "somewhat" (26 mm). No effects on pulmonary function, nasal swelling, nasal airway resistance or plasma inflammatory markers (C-reactive protein, and interleukin-6), measured before and after exposure, were seen. There was a non-significant tendency to increased blinking frequency, as measured continuously during exposure, after exposure to 10 ppm acetic acid. In conclusion, our study suggests a mild irritative effect at 10 ppm acetic acid.