In this study, the effect of four isothiazolone biocides on purified alcohol dehydrogenase was evaluated (Figure 7). The results showed that DCOIT and OIT displayed the most rapid inhibition, with near-complete reduction in activity within 15 min. CMIT and MIT showed similar effects with approximately 70% of the activity remaining after 15 min. In this case, the more hydrophobic molecules provided the most rapid inhibitory effects on the enzyme in vitro.