Dequalinium chloride undergoes photodegradation in simulated sunlight at 22 ± 1°C. The reaction follows first order kinetics, the addition of a molar equivalent of hydrogen peroxide markedly increases the rate constant of this reaction. The incorporation of non-steroidal anti-inflammatory agents as well as hydrogen peroxide results in a diminution in the rate constant. In such cases where the test drug is insoluble in water the addition of 2% ethanol to effect solubilisation changes the order of reaction to second order but still provides a means of comparing the hydroxyl radical scavenging properties of the drugs. This technique is rapid and cheap and could form a feature of the standard screening technique for novel medicinal agents.