A non-invasive saliva sample delta 9-THC radioimmunoassay has been applied to 352 samples from 25 male and 10 female marijuana users after administration of one-half to two standard cigarettes (27 mg delta 9-THC/cigarette) and 72 control negative subjects who ingested a large variety of foods, condiments, or medications in an attempt to demonstrate interferences. The shortest duration of a positive was 2 hrs and the longest was 5 hrs after administration of the cannabis. No positives occurred in control subjects.