We developed a detection apparatus, equipped with two photomultiplier tubes, for chemiluminescence from singlet oxygen: the dimol light emission (ca. 634 nm) and the monomol light emission (ca. 1270 nm). Singlet oxygen was generated by reactions between sodium hypochlorite and hydrogen peroxide and between acetonitrile and hydrogen peroxide, and the dimol and monomol chemiluminescence emission were simultaneously observed using the apparatus. It was found that the chemiluminescence of the monomol emission in the acetonitrile system was enhanced in the presence of alkali halides and lasted more than 1.5 h, while the dimol emission in the acetonitrile system and the dimol and monomol emission in the hypochlorite system were not affected by the presence of alkali halide. The effects of antioxidants and nucleosides on monomol chemiluminescence in the acetonitrile system were examined. The specific chemiluminescence of the monomol emission of singlet oxygen in the acetonitrile system in the presence of alkali halides and the initial data concerning antioxidants and nucleosides will be useful in the design of I new analytical systems or in elucidating the mechanism of chemiluminescence emission from singlet oxygen.