Preliminary observations and responses to interviews in Valencia, Spain reveal that injecting drug users (IDUs) dissolve heroin before injection with two or three drops of lemon juice. Solution in lemon juice makes heating of heroin in water unnecessary. This pattern apparently developed spontaneously in Spain, but is almost unknown elsewhere in the world. Its implications for IDUs' health remain speculative, but use of lemon juice to dissolve heroin for injection deserves further scientific study.