Abstract: A kit for detecting a first substance in a sample including a stabilized 1,2-dioxetane bearing an enzyme-labile substituent, which is destabilized and caused to decompose by contacting the 1,2-dioxetane with an enzyme under conditions which cause the enzyme to cleave the enzyme-labile group from the dioxetane, thereby yielding a negatively charged oxygen anion bonded to the 1,2-dioxetane, which causes the 1,2-dioxetane to decompose without input from an external excitation energy source, the decomposition being accompanied by chemiluminescence; and a second component selected from the group consisting of a specific affinity substance (e.g., an antigen, an antibody or a nucleic acid probe) and an enzyme which destabilizes said 1,2-dioxetane.