Resolved analogues of abscisic acid (ABA) were tested in rice seedling elongation, lettuce seed germination, barley α-amylase induction and stomatal opening in spiderwort epidermal strip bioassays. (1 S)-(+)-1 -Deoxy-1 -fluoroabscisic acid showed 1 to 1 of the activity of (1 S)-(+)-ABA and was almost equal to (1 R)-(+)-1 -deoxyabscisic acid in these assays. These results suggest that the fluorine atom cannot mimic the C-1 hydroxyl group. (1 R,6 S)-(+)-8 -fluoroabscisic acid was as effective as (+)-ABA, and the effect on the plants tested was indistinguishable from that of (+)-ABA. This result suggests that the activity of highly labile 8 -hydroxyabscisic acid is as strong as that of (+)-ABA. The activities of (-)-enantiomers were equivalent to or less than those of (-)-ABA.