Ultrasound-assisted extraction (UAE) is introduced to upper-level analytical chemistry students as a simple strategy focused on sample preparation for trace-metal determination in biological tissues. Nickel extraction in seafood samples and quantification by electrothermal atomic absorption spectrometry (ETAAS) are carried out by a team of four students. The experiment covers (i) the study of variables influencing the extraction process (sonication time, ultrasound amplitude, acid concentration, particle size, and sample mass) and the selection of optimal conditions; (ii) the determination of analytical characteristics and method validation using certified reference materials; and (iii) the analysis of seafood samples (i.e., mussels, prawns, hake, and sole). (Contains 1 table and 3 figures.)