Suspension cultures of potato and Arabidopsis were incubated with 50 microM of (+)-ABA and (-)-ABA for 3 hr. These pretreatments were found to increase the rate, by two- to seven-fold, of formation of [2H6] phaseic acid (PA) from [2H6] ABA, applied in a subsequent incubation. Pretreatment with trifluoro-ABA had a higher efficacy, increasing the rate of conversion 15-fold. Suspension cell cultures that had been dehydrated and then rehydrated in the presence of [2H6] ABA displayed a much lower enhancement of PA formation. We conclude that ABA induces its own oxidative catabolism in suspension cultures.