A method for determination of cadmium, lead and mercury in blood plasma of a domestic cat is developed. For determination of cadmium and lead, the two-step procedure is based on dry ashing of blood plasma samples and on electrothermal atomic absorption spectrometric quantitation. In the first step, samples are heated in glassy vials in atmosphere of nitrous oxides by using an APION Dry mode mineralizer. The residue of inorganic components retained in the vial is then dissolved in a minimum amount of diluted high purity nitric acid. In the second step, content of cadmium and lead is determined by graphite furnace atomic absorption spectrometry employing Perkin-Elmer Model 4110 ZL Zeeman background corrected atomic absorption spectrometer equipped with a transversally heated graphite atomizer. In order to stabilize analytes in graphite furnace, chemical modification with pre-reduced palladium and other reagents is applied. The amount of used modifiers, the temperature program and calibration mode are optimized. Mercury is determined without decomposition of samples by atomic absorption spectrometry using an AMA 254 Advanced Mercury Analyzer. Samples of blood plasma of 138 individuals were analyzed. Content of cadmium, lead and mercury in the plasma was found in the range of 0.1 - 9 µg.l^-1, 1.2 - 50 µg.l^-1 and 0.3 - 15 µg.l^-1, respectively. Limits of detection, based on 3s criterion, of 0.1 µg.l^-1 Cd, 1.2 µg.l^-1 Pb and 0.33 µg.l^-1 Hg were achieved. Results are correlated with complementary data with respect to kind (breed), sex, age, environmental conditions, and to some other veterinary diagnostic parameters (diseases, etc.).