The potential of multiwalled carbon nanotubes (MWNTs) as a solid-phase extraction adsorbent for the preconcentration of trace Cd, Mn and Ni has been investigated. The studied metal ions can be adsorbed quantitatively on MWNTs at pH 8.0, then eluted completely with 0.5 mol L⁻¹ HNO₃. The adsorption capacity of MWNTs was found to be 7.42, 4.86 and 6.89 mg g⁻¹ for Cd, Mn and Ni, respectively. A new method using a microcolumn packed with MWNTs as sorbent has been developed for the preconcentration of trace amounts of Cd, Mn and Ni prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Parameters influencing the preconcentration of the analytes, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been examined. The method has been successfully applied to the determination of trace elements in some environmental samples with satisfactory results.