A new accelerated caking test for use with urea has been developed and used in screening potential conditioning agents. The urea sample is held under pressure in a perforated cylindrical mold while temperature and relative humidity are cycled, to cause alternate absorption and loss of moisture. The degree of caking was measured by a penetrometer and was expressed as a caking index: hardness of unconditioned urea divided by the hardness of conditioned urea. Tests of 3 1/2 days duration were satisfactorily correlated with 1- and 3-month bag storage tests run at two different urea producing plants.