This chapter discusses Saint John's wort and hypericin, their therapeutic effects, and the functions of naturally occurring hypericin-like pigments in Stentor coeruleus and Blepharisma japonicum. The chapter explores the mechanism by which these pigments control cellular movements and light-induced movement responses such as photophobic response, photokineses, and phototaxes. This chapter also discusses behavioral responses to light, biology of ciliates, and chemical pathways that Stentor and Blepharisma use to convert light signals received by their pigments into physiological movement responses.