A method for the determination of bismuth in a variety of biological tissues (bovine liver and kidney, pig and human stomach, and human teeth and bone) by atomic absorption spectrometry with electrothermal atomization was developed and evaluated. Platinum (2 µg) was chosen from several potential chemical modifiers (Lu, Ni, Pd and Zr) as the most appropriate for the sensitive and reliable determination of bismuth in such samples. Addition of 10 µl of 4% (w/v) tartaric acid together with platinum improved the stabilizing efficiency of the modifier. The method included digestion of approximately 100 mg of the tissues in 1.0 ml concentrated nitric acid and 0.2 ml hydrogen peroxide 30% (w/v) under microwave radiation. The detection limits were found to be 1.80 µg l⁻¹ and about 0.1 µg g⁻¹ for aqueous standards and biological tissues, respectively, and the characteristic mass was 22 pg. The relative standard deviation varied from 3.5 to 0.8% for aqueous standards of 30 and 100 µg l⁻¹, respectively, and from 1.4 to 4.8% for the pooled samples submitted to microwave heating. The results obtained for the determination of bismuth in Seronorm^™ trace elements materials (whole blood and urine) with known added amounts of bismuth, together with good recoveries (ca. 98.7%) for added analyte to samples before and after digestion, demonstrate the applicability of the procedure to the analysis of real samples.