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Odour threshold concentrations, determined in agueous-ethanol solution, and odour qualities are reported for 18 enantiomeric and diastereomeric pairs of citronellyl derivatives [13 linear monoterpene compounds and five monocyclic α-damascone and α-ionone-related compounds (trans-2,2,6-trimethylcyclohexyl derivatives)] (98%ee). Fairly large differences in both odour strength and odour qualities were found between the monocyclic diastereomeric pairs. In four of the five cyclic compounds, the (1R, 6S)-form was found to be stronger and more sensorily active than the antipode. On the other hand, the linear enantiomeric pairs showed only small differences in both odour strength (half of them showed the same threshold values) and odour character. However, all the (3S)-forms showed milder, cleaner and a much preferable top note than the (3R)-forms except for citronellyl nitrile and the diester (citronellyl ethyl oxalate), whose (3R)-form showed a characteristic floral musk odour, although the (3S)-form showed a rose floral odour. Copyright © 2004 John Wiley & Sons, Ltd.