Objectives: Among the many chemicals used in a hair salon, exposure to thioglycolic acid (TGA) used for permanent waving solutions (PWS) potentially causes adverse health effects. However, no report has been previously published on the indoor air concentrations of TGA in a beauty salon that contributes to assessment of exposure to TGA of hairdressers and their customers. This study aimed to demonstrate the present concentration levels of TGA in indoor air of a beauty salon where the PWS containing ammonium thioglycolate was actually used for perm treatments. Methods: A field measurement of TGA, dithiodiglycolic acid (DTDGA, a reaction product of TGA and cysteine residues of hair keratin) and ammonia was carried out in a beauty salon located at Tokyo, Japan, from June 30 to July 2. Both TGA and DTDGA were collected in water using an impinger and determined by high performance liquid chromatography (HPLC). Results: The indoor air concentrations of TGA were below the limit of detection of 0.008 mg m⁻³ at every event and much lower than occupational safety guideline levels set by the NIOSH and ACGIH. Meanwhile, the concentrations of ammonia ranged from 0.15 to 0.87 mg m⁻³, and relatively higher concentrations were found during perm events and in samples collected near stations used for perm treatments. Concentrations of DTDGA varied from <0.026 mg m⁻³ to 0.75 mg m⁻³. Conclusions: There was a different emission process of TGA and ammonia from PWS, and airborne TGA is not important as a possible exposure route for hairdressers and customers in this beauty salon.