The participants were ages 12-21 years and came to the clinic at the Children's National Medical Center for routine health care. Their blinded and anonymous urine samples were tested for the presence of marijuana, phencyclidine (PCP), amphetamines, opiates, and cocaine. The analyses compared the youths from the two periods with respect to the drugs, their ages, and sex. Fourteen percent of the most recent group tested positive for 1 or more drugs; 13 percent were positive for cannabinoids. Males were significantly more likely than females to test positive for drug use. In addition, the oldest adolescents were more likely than the younger adolescents to test positive for drug use. Moreover, youths tested recently were significantly more likely than those in the earlier study to test positive for at least one drug and for cannabinoids in particular and were less likely to have urine tests positive for cocaine. Findings indicated an increase in positive urine tests in youths seen in this clinic, with a strong shift toward cannabinoids and a shift away from cocaine. Findings indicated that practitioners need to be aware that juvenile drug use patterns can shift relatively abruptly and that counseling should target current drug use patterns. Tables and 29 references (Author abstract modified)