The social problems of drug abuse are a matter of increasing global problem. Nowadays, international agencies need fresh methods to monitor trends of the use of illicit drugs. In this sense, small amounts of drugs are transferred to banknotes and they could be detected and quantified. In the current study, most of the banknotes analyzed showed detectable drug residues (92.5 percent). Cocaine was the most frequently detected drug, present in approximately 90 percent of the samples. In addition, 75 percent, 35 percent, and 15 percent of the banknotes showed residues of amphetamine derivatives, opiates, and benzodiazepines, respectively. An average of three drug residues per banknote was detected. In summary, the presence of drug residues in banknotes could be useful as a tracer for the prevalence of drugs. (Published Abstract)