Using monoclonal anti-fumonisin B1 antibody (anti-FB1) and avidin–biotin–peroxidase system, liver and kidneys of broiler chicks were evaluated for the detection and distribution of fumonisins (FBs). One hundred and fifty micrograms of FB1 or culture extract of Fusarium moniliforme str. 113F containing 150 µg of FB1 and 4 µg of FB2 were administered into the vitelline sac of 1-day old, specific pathogen-free chicks. The animals were killed 24 h after injection, and renal and hepatic tissues submitted for immunohistochemical analysis. FBs were detected in the epithelial cells of convoluted distal and proximal tubules of the kidneys, as well as in the cytoplasm of hepatocytes. This novel immunohistochemical method developed is expected to be an efficient way for monitoring the target of the FB toxins in tissues. Copyright © 1999 John Wiley & Sons, Ltd.