An electronic nose incorporating a non-speci®c sensor array of 12 conducting polymers was evaluated for its ability to monitor wastewater samples. Sewage samples collected from the inlet works, settlement tank and ®nal ef¯uent outlet over 5 months (January±May) were used to correlate the sensor responses of these samples with their corresponding 5-day biochemical oxygen demand (BOD) values. Canonical correlation analysis (a linear reduction technique) showed that the relationship between the sensor responses and BOD over the 5 months was non-linear. However, the separate analyses of subsets of these samples for shorter time periods showed that a linear relationship is apparent for time periods of 4 weeks or less, suggesting a correlation window occurs between the sensor responses and BOD. Preliminary neural network analysis supported these observations and using a three-layer backpropagation network showed that it is possible to predict BOD values from electronic nose analysis of a wastewater sample. The ®ndings suggest that electronic nose technology could be used for the noninvasive monitoring and/or control of a wastewater treatment process.