Antibodies against sterigmatocystin (St)‐hemiacetal (HA) conjugated to bovine serum albumin (BSA) by reductive alkylation were shown to cross‐react with St‐DNA adducts in a competitive indirect ELISA. The amounts of various ligands causing 50% inhibition in binding of the antibodies with the solid phase St‐HA‐keyhole limpet hemocyanin (KLH) by St, St‐guanine (St‐Guan) and St‐formamidopyrimidine (St‐FAPy) were 0.4, 10 and 17 picomoles/assay respectively. The cross‐reactivity of the antibodies with St adducts on the single‐stranded (ss) DNA and double‐stranded (ds) DNA was also compared. The amounts causing 50% inhibition in binding of the antibodies with the solid phase St by St‐Guan‐DNA (ss), St‐Guan‐DNA (ds) and St‐FAPy‐DNA (ds) were 32, 480 and 400 picomoles per assay respectively. Enzymatically hydrolyzed St‐Guan‐DNA and St‐Guan have the same cross‐reactivity with St‐HA‐BSA antibodies. The antibodies did not interact with non‐adducted DNA at concentrations up to 2 mg ml‐1. The ELISA sensitivity for St‐Guan increased 40‐ to 100‐fold when an avidin‐biotin complex was incorporated into the system.