Brevetoxins are polyether toxins produced by the dinoflagellate Karenia brevis that are released into the air and are known to cause respiratory hemorrhage in manatees and irritation in humans. Brevetoxin has been previously reported to cause DNA breakage and chromosomal aberrations in in vitro cell assays. The toxin is subject to epoxidation reaction and the formation of nucleic acid adducts in cultured lung fibroblasts and in lung tissue after intratracheal administration to rats. We have exposed rats intratracheally to brevetoxin B (45 microg/kg) and analyzed liver cells for DNA fragmentation using a comet assay. Brevetoxin B (PbTx2) treated rats showed a two to three-fold increase in the amount of DNA in the comet tails, indicating that brevetoxin has in vivo clastogenic activity. We next tested brevetoxin B for mutagenic activity using the Ames 98/100 mutagenesis assay. Brevetoxin B at concentrations from 0.064 to 200 microg/mL failed to cause histidine revertants. Oxidative metabolism of brevetoxin B resulting from Aroclor 1259-induced rat liver microsomes also failed to cause histidine revertants. Finally, direct application of the brevetoxin B epoxide (PbTx6) in the Ames 98/100 assay at concentrations from 0.064 to 200 microg/mL failed to induce histidine revertants. These studies indicate that brevetoxin B retains clastogenic activity after intratracheal administration to the rat. Although brevetoxin B has been shown to form nucleic acid adducts in the lung, neither brevetoxin B nor its epoxide metabolite has mutagenic potential as assessed by the Ames 98/100 test.