In order to investigate the distribution and excretion of sterigmatocystin, a carcinogenic mycotoxin, radioactively labelled compound was studied in rats. The highest concentration of radioactivity in serum appeared 3 h after administration of 0.5 microCi/g bw. The half-lives of distribution and excretion were 0.51 h and 43.9 h, respectively. The radioactivity was concentrated mainly in liver, stomach, kidney, duodenum and lung and to a lesser extent in fat, muscle, testis, rectum and bone. By 48 h, 56.4% had been excreted in faeces and 20.1% in urine. Biliary excretion may be the major route of excretion of sterigmatocystin.