A method for using thiazine dyes, especially methylene blue, alone or in combination with low levels of light, to selectively inactivate or inhibit intracellular replication of specific viruses, especially human immunodeficiency virus in vitro and in vivo. Examples of useful thiazine dyes are methylene blue, azure A, azure C, toluidine blue O, and thionine. The preferred dye at this time is methylene blue. Methylene blue is FDA approved for topical, i.v., and oral administration, and has minimal side effects. Since methylene blue absorbs in the red wavelengths, i.e., approximately 670 nm, which penetrates tissue much better than other lower wavelengths, light penetrating the skin to the capillaries at the surface can be used to enhance the activity of the dye.