A study has been made of mineral-acid interferences in the trace element determination of Fe, Mn and Zn by inductively coupled plasma optical emission spectrometry. A number of solutions containing 50 µg ml−1 of analytes in acid concentrations of 0 to 50% (v/v) were used. It has been found that HNO3 and H2SO4 depresses the emission signal of the analyte elements. These effects are neither caused by the change in aerosol flow rate nor the amount of aerosol reaching the plasma.