Abstract: Nonmetallic tetrapyrrole molecules are shown to catalyze the production of light by chemiluminescence in the presence of a signal solution at a pH from about 10.0 to about 14.0, having an appropriate oxidant or combination of oxidants and a luminescent reactant. The addition of an electron transport facilitator, a surfactant, a carbohydrate, and a chelating agent to the signal solution increases the output of light. These tetrapyrrole molecules are used alone or attached to haptens or macromolecules and are utilized as labels in the preparation of chemiluminescent, homogeneous or heterogeneous assays. They are also used in conjunction with other chemiluminescent label molecules to produce multiple analyte chemiluminescent assays. A chemiluminescent signal solution which comprises at a pH ranging from about 10.0 to about 14.