Several parameters of the nalorphine test for narcotic use were evaluated in prisoners with histories of prior narcotic use. Measurement of changes in pupillary diameter caused by narcotics alone or in combination with narcotic antagonists was correlated with chemical analysis of the urine for narcotics or metabolites. After one dose of morphine, the pupillary test remained positive about 4 hours, while urinalysis usually detected a single dose for as long as 36 hours. However, when morphine was administered every 6 hours for 5 days, some sub;ects gave positive pupillary tests 20 hours after the last dose. Negative pupillary tests were obtained after as many as three doses of codeine, but when codeine was given every 6 hours for 5 days more positive tests were obtained each day. Positive pupillary tests were obtained 2 to 4 hours after single in;ections of meperidine, heroin, and oxycodone, and 6 hours after methadone. The pupillary test is a useful method of screening for narcotic use, which might well be combined with chemical tests for narcotics in the urine.