Giving students the opportunity to extract, manipulate and visualise DNA molecules enhances a constructivist approach to learning about modern techniques in biology and biotechnology Visualisation usually requires agarose gel electrophoresis and staining. In this article, we report on an alternative DNA stain, Nile Blue A, that may be used in the classroom to visualise DNA. The stain is inexpensive, is at least as sensitive as methylene blue, does not require destaining, requires visualisation with only visible light, and is specific for DNA but not RNA. (Contains 4 figures.)