A combination fluorescence-gas chromatog. method for improving the reliability of large volume mass drug screening procedures is described.The smallest detectable quantity of the various drugs in urine with the method is as follows: morphine (I) [57-27-2] and quinine [130-95-0], 0.2 μg/ml, and methadone [76-99-3], cocaine [50-36-2], codeine [76-57-3], amphetamine [300-62-9], methamphetamine [537-46-2], and barbiturates, 1 μg/ml.