The mycotoxin fumonisin B1 (FB1) was dosed as 14C-labelled FB1, to male vervet monkeys (Cercopithecus aethiops) both by intravenous (i.v.) injection (2 monkeys, dose 1.72 mg [86 kBq]/kg body weight) and by gavage (2 monkeys, dose 6.42 mg [321 kBq]/kg body weight). Excreta were collected over a 24-hr period, whereafter the monkeys were sacrificed and selected organs and contents of the gut collected to determine the distribution of the 14C-label. The bulk of the radioactivity recovered from tissue was found in the liver (mean of 1.92% in i.v.-dosed monkeys; 0.64% in gavage-dosed monkeys). Of the other organs analysed, the following mean amounts of radioactivity were recovered in organs of i.v.- and gavage-dosed monkeys, respectively: muscle, 0.62% and 0.14%; kidney, 0.37% and 0.03%; brain, 0.08% and 0.02%; lung, 0.07% and 0.03%; heart, 0.04% and 0.01%; spleen, 0.02% and < 0.01%; plasma, 0.66% and 0.12%; red blood cells, 0.11% and 0.01%; while a further 68.1% and 64.0% were recovered in excreta, bile, and the gut contents. Analysis of faeces and gut contents showed that radioactivity was due to FB1, its partially hydrolysed metabolites, and trace amounts of the fully hydrolysed aminopentol moiety. Analysis of bile showed an absence of hydrolysis products, indicating that hydrolysis occurred only in the gut, resulting in the removal of the tricarballylic acid moiety at the C14-position. Determination of FB1, levels in plasma following a gavage dose indicated that only limited amounts of FB1 were absorbed, as plasma levels peaked after 1-2 hr with levels below 210 ng/ml.