The objective of this investigation was to find the most reliable acid extraction method for the determination of the total metal content in a waste sample. Samples of bottom ash from a municipal solid waste incinerator and slag generated by electric arc vitrification of the bottom ash were investigated. Acid extraction methods were applied using the reagents nitric acid, aqua regia, hydrofluoric acid and a combination of aqua regia and hydrofluoric acid. Another experimental variation was whether the sample was milled prior to extraction or not. Extractants were analyzed by atomic absorption spectrometry (AAS). The data were evaluated statistically including both Welch's equality test and partial least square analysis. The main conclusion was that bottom ash was most completely decomposed by milling followed by treatment with aqua regia and hydrofluoric acid. For slag, this method was only superior with respect to the extraction of Pb and Cd. Another observation was that electric arc vitrification causes the removal of Zn, Cd and Pb which was probably due to evaporation.