Methods using chemiluminescent label compounds and chemiluminescent labeled conjugates are provided. The compounds comprise an acridan ring bearing an exocyclic ketene dithioacetal group and further contain a labeling substituent which permits attachment to compounds of interest. The novel chemiluminescent compounds and labeled conjugates are convenient to prepare, are highly stable, and generate chemiluminescence rapidly on demand. The compounds and conjugates are useful in assays of an analyte in a sample and in assays employing labeled specific binding pairs.