Knowledge of the nature and behavior of benzotriazole (BTA) towards antiquities is summarized. Experimental preparations of stable insoluble BTA complexes with cuprous and cupric salts are usually made in water. Treatment by conservators, however, may utilize ethanol solutions and the resulting complexes may be different unless water is always available to enter into the complex. Tests suggest that bare metal is best treated in 1% aqueous BTA at 50 C. Heavy corrosion crusts may be treated equally well in alcoholic as in aqueous solution. Experiments on bare metal surfaces suggest six hours immersion at room temperature for full effectiveness but corroded objects that do not respond may be immersed for two to six months in 1% aqueous or 3% ethanolic BTA. Difficulties with vacua and the health hazards of BTA, especially at elevated temperatures, were also noticed. Author's address: University Museum, 33rd and Spruce Sts., Philadelphia, Pa., 19174, USA.