A commercial microwave acid-digestion system employing three types of closed vessels, a pressure-relief PFA-Teflon bomb (A), a pressure-relief Berghof all PTEE bomb (B) and a completely closed Parr microwave acid digestion bomb (C), was evaluated for sample digestion prior to the determination of trace elements in a biological tissue. The digestion procedure was based on sample dissolution with an HNO3-H2O2 mixture using microwave heating. The resulting solutions, analysed by flame and graphite furnace atomic absorption spectrometry, showed good agreement for all three closed-vessel techniques. Sample preparation time was approximately 10 min for vessels B and C, and 15 min for vessel A (including subsequent cooling time and preparation of the final solution).