The effects of spraying lead arsenate on the activities of citrate synthase (CS ; EC 4.1.3.7), NAD-isocitrate dehydrogenase (NAD-IDH ; EC 1.1.1.41), and phosphoenolpyruvate carboxylase (PEPC ; EC 4.1.1.31) in the juice sacs of fruit of 'Natsudaidai' (Citrus natsudaidai Hayata) were investigated. Citrate accumulation in the juice sacs was significantly inhibited from early September through January by spraying lead arsenate solutions over tree canopies on June 4 and July 2. Lead arsenate treatment enhanced CS activity during late July and November and NAD-IDH activity after early August, but it did not affect PEPC activity. These results suggest that lead arsenate accelerates TCA metabolic cycle but does not promote a substrate supply to the TCA cycle. This resulted in a reduction of citrate transport to the vacuole and in a repression of citrate accumulation.