Synthesis of the five mono- and di-hydroxylated metabolites of the aryl hydrocarbon receptor high affinity ligand 6-formylindolo[3,2-b]carbazole is described. The structures of the metabolites were unequivocally established as 2-hydroxy-, 8-hydroxy-, 2,10-dihydroxy-, 4,8-dihydroxy- and 2,8-dihydroxyindolo[3,2-b]carbazole-6-carboxaldehyde.