Flame atomic absorption spectrometry (AAS) has been used to measure magnesium (Mg2+) and potassium (K+) contents of wistar rat myocardium and skeletal muscle. Ten to twenty mg of tissue was homogenized in 10 mM hydrochloric acid, centrifuged, and the clear supernatant was diluted three-fold in deionized distilled water before determination of Mg2+and K+concentrations. The calibration curves of both ions were linear from 0.25 to 2.0 mg/L for Mg2+and from 1.5 to 15.0 mg/L for K+. The mean values (±SD) of Mg2+and K+contents for the analyzed cardiac muscle were 371.97±12.16 mg/Kg of wet tissue with a coefficient of variation (CV) of 3.3%, and 4571.02±359.74 mg/Kg with CV of 7.9%, respectively. Those for various skeletal muscles varied between 323.35-420.60 mg/Kg Mg2+, with CV ranging from 3.2% to 8.7%, and 4883.84-8156.68 mg/Kg K+, with CV ranging from 4.4% to 10.1%. The within-day CV were 2.8% to 3.8% for Mg2+and 3.2% to 5.9% for K+, whereas day-to-day CV were 6.2% to 10.2% for Mg2+and 8.7% to 10.5% for K+. Recoveries were 92.7% to 104.9% for Mg2+, and 93.2% to 106.1% for K+. Values for Mg2+ obtained by the proposed method were significantly different from those obtained by a published tissue digestion method, those for K+were not significantly different.