The urinary excretion patterns of morphine and codeine in a number of individuals following consumption of morphine-based narcotic drugs have been studied. From the data collected the relative amounts of codeine and morphine in urine specimens were compared and certain trends, consistencies and irregularities were revealed. To a certain extent, the ratio of the proportion of codeine to morphine excretion in urine may be used to determine the nature of the drugs consumed. This correlation is useful in the interpretation of the results of urine analysis which is the basis of effective control and rehabilitation of drug addiction.