Methods for generating chemiluminescence rapidly by reaction of at least one compound comprising a C--C double bond substituted at one carbon with two sulfur atom-containing groups with a peroxidase enzyme and a peroxide are disclosed. The chemiluminescence thus produced can be used as a detectable signal in assays for peroxidase enzymes or peroxide-producing enzymes and in assays employing enzyme-labeled specific binding pairs. Use of the methods provides rapid signal generation, achieving a plateau intensity in under one minute. The substrate can be provided in a composition which demonstrates unexpectedly long storage stability.