This article describes the employment of a novel p-phenol derivative, 4-(1,2,4-triazol-1-yl)phenol (TRP), as a highly potent signal enhancer of the luminol-hydrogen peroxide (H(2)O(2))-horseradish peroxidase (HRP) chemiluminescence (CL) system. The CL reaction conditions were optimized, and the enhancement characteristics of TRP were compared with those of p-iodophenol (PIP). TRP produced a strong enhancement of the CL with the effect of prolonging the light emission. The developed system was then applied to the determination of H(2)O(2) with immobilized HRP using magnetic beads as a solid support. The linear range for H(2)O(2) was 2.0x10(-6) to 1.0x10(-3) M. The detection limit for H(2)O(2) was 2.0x10(-6) M. The proposed sensor was applied successfully to the determination of H(2)O(2) in rainwater.