Cows' urine was analysed by gas chromatography mass spectrometry (GC-MS). The profiles from preovulatory, ovulatory and postovulatory samples were compared to establish any qualitative and quantitative differences that might have potential value in olfactory communication. Dichloromethane was used as the solvent for extraction of the compounds. Seven different compounds were detected, of which only two were common to all the chromatograms. The chemical profile of oestrous urine was distinguished by the presence of two specific compounds, viz. di-n-propyl phthalate and 1-iodoundecane, that were not found in the other samples. As oestrous urine has been shown to elicit sexual behaviour in cattle, these two characteristic peaks may represent important chemical compounds that elicit signals that allow the bull to detect 'oestrous odours'.