The polarographic determination of benzaldehyde was carried out in a wide range of pH values using partial least squares (PLS) regression to analyse signals obtained as a result of complex processes. In the electrochemical reduction of benzaldehyde at mercury electrodes, several chemical (proton transfer and dimerization) and electrochemical reactions take place, depending both on the concentration of benzaldehyde and pH. This interferes seriously in the quality of the recorded analytical signals, causing the shift and overlapping of the polarographic peaks. The multivariate technique used models these interferences and allows the successful determination of this organic compound independently of the shape of the signals and the pH of the medium in the concentration range analysed, the mean absolute relative errors being equal to 2.10%.