This document discusses non-radioactive labeling of probes for DNA and RNA detection. It describes using a double-stranded DNA probe where one strand is biotin-labeled to bind to the desired DNA sequence. After washing away unbound probe, alkaline phosphatase and avidin are added, where avidin binds strongly to biotin. When a chemiluminescent substrate is added, only DNA regions with the bound probe will illuminate on x-ray film or phosphor imaging, allowing visualization of the desired sequence without radioactivity and at lower cost.