Data were gathered from July 1999 to June 2001. Urine samples were collected from 1,161 persons detained in police custody for a criminal offense at either Parramatta (608 persons) or Bankstown (553 persons). Of the arrestees that participated in the urinalysis testing, 69 percent of persons tested positive to at least one drug type. Cannabis was the drug most commonly used by detainees with 45 percent of the sample testing positive. The next most commonly used drugs were opiates (38 percent) and benzodiazepines (22 percent). Cocaine was the drug for which the fewest number of detainees tested positive, with only 6 percent of the sample showing traces of this substance. The urinalysis tests confirmed that more than half of the detainees with a positive drug test result had used more than one drug type recently. More than one in five of all detainees (21.4 percent) tested positive to two drugs, while about the same proportion (21.7 percent) tested positive to three or more drugs. Dangerous combinations of drugs occurred among a sizeable proportion of the detainees. Multiple drug use can increase the risk of overdose, and affect users physically and mentally. This study shows that a significant proportion of police detainees and the police that deal with these detainees are exposed to risk from the high level of multiple drug use described. It is noted that neither Bankstown nor Parramatta are representative of either Sydney or New South Wales. 3 figures, 2 tables, 4 references