Background and Aims: The aim of this study was to determine the cause of taints and off-flavours in a number of commercial wines and to develop methods for quantitative analysis of the compounds responsible. Methods and Results: Three compounds, 2-chloro-6-methylphenol (i.e. 6-chloro- ortho-cresol), 2,6-dichlorophenol and indole, were identified by gas chromatography (GC)/mass spectrometry (MS)/olfactometry as causes of taints or off-flavours in the wines. New methods for quantitative analysis of these three compounds, as well as some other chloro- and bromophenols were developed. The methods employed GC/MS and stable isotope dilution analysis, and confirmed the presence of 2-chloro-6-methylphenol, 2,6-dichlorophenol and indole in some wines at concentrations well above their odour and taste detection thresholds. Conclusions: 2-Chloro-6-methylphenol, 2,6-dichlorophenol and indole were confirmed as causes of taints and off-flavours in commercial wines. Significance of the Study: The development of new analytical methods will make it possible to determine whether chlorophenol (and perhaps also bromophenol) taint in wine is more widespread than previously recognised. Similarly, the simple, rapid and accurate method for quantifying indole in wine will allow large numbers of wine and ferment samples to be studied to determine those factors that can result in unacceptably high concentrations in commercial wines.