What does Hoechst stain?

Hoechst dyes are blue fluorophores. There are 3 related Hoechst dyes, Hoechst 33258, Hoechst 33342, and Hoechst 34580. Hoechst 33258 and Hoechst 33342 are the most commonly used. Hoechst dyes are used to stain DNA in living and fixed cells by binding to adenine-thymine-rich sequences of the minor grove in DNA. They are compatible with immunohistochemistry applications.

Compared to Hoechst 33258, Hoechst 33342 is significantly more cell-permeable and is usually preferred for living cell staining. Hoechst 33358 is the preferred dye to stain fixed or dead cells.