The action of sunlight on dilute (1–10 ppm) aqueous solutions of the herbicide bromacil (5-bromo-3-sec-butyl-6-methyluracil) resulted in the formation of only one detectable photoproduct, 5-bromo-6-methyluracil, in very low yield. The almost quanitative recovery of starting material, even after prolonged periods of irradiation, indicated that bromacil was very stable toward sunlight. TheN-dealkylated photoproduct proved to be much less stable toward sunlight wave-lengths, forming principally 6-methyluracil. No 5-bromouracil was detected.