The effects of carvone on the locomotion activity (LA) of mice depends on the chirality of this terpene ketone and the circadian rhythm of mice, the latter assessed by using a light-barrier cage upon administration of analeptics and sedative drugs. (-----)-Carvone, the so-called 'spearmint carvone', showed more sedative and relaxing effects, whereas (+ + + + +)-carvone, the 'caraway carvone', demonstrated both sedation and activation effects on the LA of mice, e.g. (-----)-carvone showed only in amphetamine pre-treated 'morning mice' a relaxant effect, while with other analeptics pretreated mice nearly no alteration of the LA could be observed. (+ + + + +)-Cavone slightly counteracted the stimulating effect of LA with metamphetamine, phenobarbital and cathine pre-treated 'morning mice', but decreased the LA when the mice were pre-treated with other analeptics, especially amphetamine. Mice in the resting phase showed a similar reaction upon sniffing (-----)-carvone as before; only pre-treatment with caffeine led to a stimulation. In the late morning a moderate reduction of the animal's LA upon sniffing (+ + + + +)-carvone vapour was observed after pre-treatment with most of the analeptics, except with amphetamine, where strong over-agitation could be counteracted entirely.