The rate of disappearance of hydroxyl radicals (generated by H+NO2 → OH+NO) along a discharge flow tube both with and without ethene present was measured by resonance fluorescence. Stoichiometry was simultaneously measured with a mass spectrometer, the leak into which was located downstream of the resonance fluorescence cell. After allowing for loss of hydroxyl by known homogeneous reactions and for wall loss (when applicable) it was found that for OH+C2H4 the low pressure limiting third-order rate constant kter was (3.1 � 0.5)x 10-29 cm6 s-1 at approximately 298 K. In addition an estimate for the second- order rate constant for OH+OH was obtained, namely (1.7 � 0.2) × 10-12 cm3 s-1. These results are discussed in relation to previous measurements.