Bisbenzimide (Hoechst 33342) is an organic compound used as a fluorescent stain for DNA in molecular biology applications.

[1] Several related chemical compounds are used for similar purposes and are collectively called Hoechst stains.

Bisbenzimide tends to bind to adenine–thymine-rich regions of DNA and can decrease its density.

Bisbenzimide mixed with DNA samples can then be used to separate DNA according to their AT percentage using a cesium chloride (CsCl) gradient centrifugation.