Adding biocides to dispersion products is a well-known practice to control microbial deterioration. Isothiazolones are among the most commonly used preservatives, in particular a mixture of 2-methyl-2H-isothiazol-3-one (MIT) and 5-chloro-2-methyl-2H-isothiazol-3-one (CIT). In recent years, for health reasons, due to its strong sensitizing effect, CIT has been replaced by 1,2-benzisothiazol-3-one (BIT). Furthermore, numerous products are now available for interiors containing the fungicidal active substance 2-octyl-2H-isothiazol-3-one (OIT). So far nearly nothing is known of the emission behavior of BIT and OIT. An analytical method was developed for these two isothiazolones and interior products containing BIT respectively OIT have been investigated in an emission chamber and in test rooms. The chamber tests revealed maximum concentrations of 6.7 μg OIT/m3, 1.9 μg BIT/m3, and 187 μg MIT/m3. Concentrations obtained in the test rooms were at levels up to 1.4 μg OIT/m3 and 29 μg MIT/m3. A noticeable finding was the very slight subsidence of OIT and BIT levels over several weeks. While MIT outgassed quickly, OIT in particular showed low concentrations, but prolonged evaporation.