Traces of cocaine can be found on 94% of euro banknotes circulating in Spain, a study has suggested.
Euro notes seem to be popular with cocaine users
Analysis of notes from a selection of Spain's major cities showed that each one carried an average of 25.18 micrograms of cocaine.
Spain has one of the highest rates of cocaine use in the world, with about 475,000 regular users, El Mundo newspaper reports.
Euro banknotes have only been in circulation since January 2002.
Scientists could not carry out tests on old peseta banknotes before 2002 for fear that they would not withstand the chemicals used in the analysis.
Now, though, armed with resilient modern euro notes, experts collected 20 notes for analysis from each of five cities - Barcelona, Bilbao, Madrid, Valencia and Seville.
From each city they gathered five 10 euro notes, 10 of 20 euros and five of 50 euros.
Only three of the notes gathered from each of Madrid and Barcelona were found to carry no trace of cocaine.
Users of the drug usually snort it by rolling up a banknote into the shape of a tube.
But experts said it was difficult to tell which notes had been used for snorting cocaine and which had become contaminated with the drug in other ways, such as in counting machines.
According to El Mundo Spain has just over one billion banknotes in circulation, with estimates suggesting that 142 million have been used directly to snort the drug.
Other countries have been found to have drug problems in the past: a BBC survey in 1999 found that 99% of £5 notes tested in London contained traces of cocaine.
Euro banknotes in Germany appear especially vulnerable: a 2003 survey gave similar results to the Spanish analysis about cocaine traces.
And this month officials in Germany suggested that methamphetamine, or crystal meth, could be causing euros to "corrode" when users snort it through a rolled-up note.