Recent demonstrations of chloroquine retinopathy suggest the need for re-evaluation of the drug's therapeutic efficacies as compared with toxicity. This review attempts to summarize the portion of the massive chloroquine literature most pertinent to dermamatology. Mode of Action The mode of action of chloroquine remains poorly understood. Granuloma pouches produced by air and croton oil in guinea pig skin treated by chloroquine demonstrate an anti-inflammatory mechanism different than that of corticotropin, cortisone, or the salicylates.1In addition, therapeutic action is not related to adrenal cortical function.2,3Chloroquine does not act as a sun-filtering agent systemically, but may suppress a specific photoallergic response.4The claim that chloroquine's structure resembles riboflavin and apresoline has led to an intriguing hypothesis5; such speculation has not been useful. There are many theories as to mechanism of action, but none is proved.6,7 Distribution and Excretion Urinary excretion of chloroquine is slow,