Arsenic speciation analyses were performed on freeze-dried fish muscle tissues using ETAAS, prior to applying modified reported method (Korenovska & Suhaj, 2005). The accuracy of methodology was checked by CRM DORM-2 for total As, while due to unavailability of certified values of both As species, standard addition method was applied by spiking known amount of As3+ and As5+ in real sample. Triplicate sub samples of lyophilised muscle tissues (0.2 g) were spiked with standards of both As species at three concentration levels, before treatment. The Quantitative recoveries were obtained for 102 ± 3% and 100 ± 5% for As3+ and As5+, respectively (Table 2). These values are evidence for the excellent performance of the methodology used for speciation of inorganic arsenic. The precision of the techniques, expressed as the relative standard deviation (%RSD) of a minimum of six independent analyses of the same real sample, was observed as 1.90 and 3.92 for As3+ and As5+, respectively.