Fumonisin B1 (FB1), a toxic and carcinogenic secondary metabolite of the fungus Fusarium moniliforme Sheldon, was administered either by i.v. injection or by gavage to vervet monkeys (Cercopithecus aethiops). FB1 dosed by i.v. injection to two female vervet monkeys was rapidly eliminated from plasma with a mean half-life during the elimination phase of 40 min. Analysis of urine and faeces over a 5 day period after dosing gave an average 47% recovery of the dose as FB1 and its hydrolysed analogues. Two female vervet monkeys were given a single gavage dose of 14C-labelled FB1. During the subsequent 3 day period, faecal excretion of radioactivity accounted for an average of 61% of the administered dose and urinary excretion 1.2%. Residual radioactivity was recovered in low levels from skeletal muscle (1%), liver (0.4%), brain (0.2%), kidney, heart, plasma, red blood cells and bile (each 0.1%), while the contents of the intestines accounted for a further 12% of the radioactive dose. In total, 76% of the administered radioactivity was recovered. Analysis of the faeces, intestinal contents and urine indicated that over 90% of the radioactivity in these samples was due to FB1 and its hydrolysis products.