Certain furanoquinolines of the Rutaceae and a number of the widely distributed beta-carboline or harmane alkaloids are photosensitizers in near ultraviolet light (320-400 nm). These compounds have been shown to be phototoxic to yeasts and bacteria. In addition, two canthinones of the Rutaceae and the N-methylpyrolidine substituted harmane alkaloid, brevicolline (from Carex), display phototoxicity towards bacteria and fungi in near ultraviolet light. All of these alkaloids are phototoxic to Chinese hamster ovary cells, inhibiting mitosis and causing gross chromosomal changes. The target for their phototoxicity appears to be the cell nucleus.