The validity of self-reported drug use information is often questionable, particularly if there is a real or perceived consequence to what is reported. Urinalysis is a critical variable in treatment research; it is an objective measure that is independent of problems of subject memory or veracity. But urinalysis also has some limitations. A drug must be present in the body in order for it to be detected, so there is a relatively narrow window of time during which drug use can be detected by urinalysis. Clinical evidence suggests also that qualitative urine tests may be insensitive to moderate changes in drug use. Changes in the pattern, frequency, and amount of use that are not apparent from qualitative urinalysis might be discernible from quantitative urinalysis. However, quantitative urine testing is somewhat more expensive and urine drug/metabolite concentration can be affected by such variables as the time between drug use and urine collection, fluid intake, and individual metabolic differences. Tables, figures, references