The photochemistry of N-hydroxypyridine-2(1H)-thione (N-HPT) has been investigated in aqueous and organic solvents using laser flash photolysis (lambda(exc) = 308 or 355 nn). Independent of the environment, UV excitation of N-HPT causes homolytic N-O bond cleavage, which leads to formation of the 2-pyridylthiyl (PyS(.)) and hydroxyl((OH)-O-.) radicals. In aqueous media, this process occurs efficiently from both the anionic and neutral forms (Phi(N-O) approximate to 0.20-0.30). In addition to N-O bond scission, N-HPT undergoes other primary photoprocesses which are pH-dependent. At pH = 7, photoionization (Phi(e-) = 0.09 (lambda(exc) = 308 nm) and 0.05 (lambda(exc) = 355 nm)) of the anionic form generates the hydrated electron as well as the semioxidized radical of N-HPT. Fast rearrangement of the latter species produces the N-oxy-2-pyridylthiyl radical. At pH = 2, where the uncharged structure predominates, formation of an excited triplet state (E(T) greater than or equal to 59.5 kcal mol(-1)) is observed (Phi(T) greater than or equal to 0.05 using lambda(exc) = 355 nm) but photoionization does not take place. The neutral form of N-HPT displays similar photochemical behavior in organic solvents, generating (OH)-O-., PyS(.), and the triplet state (Phi(N-O) = 0.30-0.45 and Phi(T) = 0.03-0.05 using lambda(exc) = 355 nm). In nonpolar, aprotic media, the subsequent reaction of PyS(.) with the thiol tautomer of N-HPT leads to the formation of an unsymmetric disulfide radical. Reactivities of the different transient species toward potential scavengers have also been investigated. The results obtained show that the simultaneous generation of several highly reactive intermediates is a major drawback in the use of N-HPT as a clean and simple photolytic source of (OH)-O-..