N-Acetylcysteine (NAC) is known to decrease the exacerbation rate in patients with chronic bronchitis. It has also been shown that NAC has both an oxygen-radical scavenger and a heavy-metal chelating effect in high intravenous doses. In a study lasting 5 weeks, 10 healthy volunteers were treated with NAC 200 mg t.d.s. for two weeks. The concentrations of trace metals (Ca, Mg, Fe, Zn & Cu) in plasma were measured weekly and daily in a morning spot urine during the investigation. No significant change in plasma concentration or excretion was found during the two weeks of treatment, implying that additional administration of trace metals is unnecessary for patients treated perorally with a therapeutic dose of NAC.