1-Naphthol was reactive toward direct photolysis in buffered aqueous solutions (at pH 7, halflife in sunlight was about 90 min) and in cyclohexane (halflife about 15 min). The reaction rate in water increased with pH. The mechanisms of the principal photolysis pathways in both solvents did not involve singlet oxygen. In aqueous solution, the major ether-extractable product, lawsone, may have been formed by a radical process involving 1,2-naphthoquinone and superoxide as intermediates. In cyclo-hexane, most of the photolysis products observed were very polar. Several oxygen-containing compounds derived from the solvent were also observed. In a two-phase system including cyclo-hexane and pH 7 buffer, the photolysis appeared to proceed by independent mechanisms in both phases, but intermediate polar products formed in the organic layer diffused into the aqueous layer. In a system containing a surface-active material, SDS, the rate of photolysis decreased; the photoproducts were typical of those observed in cyclo-hexane rather than water.