Irradiation of double-stranded DNA solutions containing 8-methoxypsoralene /8-MOP/ by near ultraviolet light /365 nm/ resulted in the formation of fluorescent photoaddiucts 8-MOP-DNA. The fluorescence of these products in the DNA molecule is considerably quenched due to the intercalation between the bases. After hydrolysis of DNA the quenching was eliminated. The maximal fluorescence of the photoadducts was observed near 460 nm; the maximal excitation was near 328 nm.