We used accelerator mass spectrometry (AMS) and 26AI to study the plasma concentration, urinary excretion, and retention in bone, brain, and liver of a single dose of a dietary concentration of aluminum ingested either with or without citrate by 2-month-old Wistar rats. In the absence of citrate, cumulative urinary excretion and skeleton retention were each approximately 0.05% of the total 26AI dose ingested. 26AI retention in brain and liver were approximately 4 x 10(-8) and 2 x 10(-6), respectively. Concomitant citrate intake increased these median values by about two- to fivefold, although this factor was highly variable in individual rats. Independent of citrate administration, 90% of the 26AI excreted in urine (measured cumulatively over 30 days) was excreted within the first 48 h. Uptake by bone was rapid (approximately 1 h) and permanent over the 30-day duration of the experiment.