Colorimetric immunoenzymatic procedures using monoclonal antibodies to detect 5-bromo-2-deoxy-uridine-DNA in hybridization experiments are not sensitive enough. We have developed a chemiluminescent immunodot assay to improve the sensitivity of the immunoenzymatic procedure, and attained a suitable detection level for single-stranded DNA. This new chemiluminescent immunodot assay has also been used to detect our recently synthesized cytidine analogue by means of its corresponding monoclonal antibody.