A novel hypocrellin congener, 2-butylamino-2-demethoxy-hypocrellin B (2-BA-2-DMHB) was found to be an effective photosensitizer. Compared with its parent compound hypocrellin B (HB), its absorption bands extended toward longer wavelength and the extinction coefficients raised to some degree (lambda(max) (nm) (log(epsilon)): 463 (4.06), 583 (4.09), 621 (4.10) for 2-BA-2-DMHB and 466 (4.06), 548 (3.70), 580 (3.52) for HB). And it also had a much higher photopotentiation factor than HB (i.e., more than 250 versus 10 at a dose of 24 J cm(-2) of red light on HeLa cells). This might be correlated to the higher ability of superoxide anion generation and the higher cellular uptake of 2-BA-2-DMHB. Meanwhile, the examinations of Hoechst 33342-labeled nuclei, DNA fragmentation on agarose gel and flow cytometry showed that 2-BA-2-DMHB induces apoptosis in photosensitized HeLa cells more quickly than HB, which might be correlated to the higher cellular uptake of 2-BA-2-DMHB and the difference of their cellular localization. The study suggested that 2-BA-2-DMHB was a well-suited candidate for a new generation of photodynamic therapy photosensitizer.