Singlet molecular oxygen [O-1(2) ((1)Delta(g))] is generated cleanly in aqueous solution upon irradiation of a heterogeneous complex, meso-tetra(N-methyl-4-pyridyl)porphine (1) adsorbed onto porous Vycor glass (PVG). The cationic photosensitizer 1 tightly binds onto PVG and gives a stable material, which does not dissociate 1 into the surrounding aqueous phase. The production of O-1(2) was measured by monitoring the time-resolved O-1(2) ((1)Delta(g)) phosphorescence at 1270 nm. Indirect analysis of O-1(2) generation was also carried out with the photooxidation of traps-2-methyl-2-pentenoate anion, which afforded the corresponding hydroperoxide. Sensitizer-1-impregnated PVG gives rise to a new singlet oxygen generator but more importantly provides a heterogeneous system for use in water.