AbstractQuenching effects of purine and pyrimidine derivatives on the extra‐weak chemiluminescence (CL) derived from the Maillard reaction of L‐lysine with D‐arabinose were investigated The pyrimidine derivatives 2′‐deoxy cytidine, uridine, and uracil quenched the CL. Cytidine did not quench the CL. Purine derivatives, e.g. uric acid and 1‐methyl adenosine were particularly effective in quenching the CL. 5‐Methyl adenine and xanthine also quenched the CL, but adenosine had no effect. A comparison of the CL‐quenching abilities of compounds that have common basic structure was made; those with ribose at the 5‐position were the strongest quenchers. A linear relationship between CL‐quenching activity and the HOMO energy of the pi orbital for the various