In this work, we studied the chronesthesia of 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3), cobalt (II) chloride and of the complex [CoCl 2 (1,25(OH) 2 D 3) 4]. The study was carried out in spring and autumn on AP and ?-GT activities in brain and kidney of rats during the rodents' active period. In rat brain, in both seasons, 1,25(OH) 2 D 3 enhanced AP activity by 59 % in spring and 21 % in autumn and ?-GT by 39 and 35 % respectively. Cobalt (II) stimulated AP activity by 34 and 29 % respectively. The complex was mainly active on ?-GT activity (70 and 36 %) showing a synergic effect on ?-GT activity in June. In rat kidney, during spring, the induction of AP activity for 1,25(OH) 2 D 3, cobalt (II) chloride and their complex was, respectively 21, 18 and 12 %. The ?-GT activity was not modified during this period, whereas in autumn, it was inhibited by –33, –50 and –28 %. The AP activity in autumn was not altered. We conclude that the effects on the two enzymatic markers of the three compounds 1,25(OH) 2 D 3, cobalt (II) chloride and [CoCl 2 (1,25(OH) 2 D 3) 4] are quite different in Spring and Autumn, and this is explained on the basis of chronesthesia.