The extension rate of the first inflorescence node of four Arabidopsis ecotypes was measured during light/dark or continuous 1ight exposure and was found to exhibit oscillations that showed various ultradian rhythms. During the processes Arabidopsis ecotypes growth rate displays ultradian rhythms with periods in the range of 18 to 72 min. The rate oscillations were not in relation with mechanical noise or environmental oscillatory conditions. Indeed, our studies suggest that the oscillations in growth rate are endogenous in their origin. Moreover than ultradian oscillations, each ecotype displayed special growth rate variations, after the transition from light to dark or reciprocally. This could be assimilated as individual growth rate signature for the four different ecotypes.