Abstract: Traces of chromium and vanadium in biological samples were determined by ICP-MS using the hexapole collision cell technique. Gas mixture of He and NH3 in the proportion of 93 to 7 was introduced into the collision cell to eliminate effectively the interferences of molecular ions of ArC+,NCl+,ClO+,ClOH+ and etc. to the determination of ultra-trace amounts of chromium and vanadium,and thus the detection limits (D.L.) of the method were lowered. The values of D.L. (3σ) were found as: for vanadium 0.005 0 μg·g-1,and for chromium 0.001 8 μg·g-1. A comparative study was made on the treatment of sample by the dry ashing method and the wet digestion method,and as shown by the results obtained,no significant difference was found. Precision tests,made on different concentration levels,gave values of RSD′s (n=12) in the ranges of 3.25%-14.08% (for vanadium) and of 4.20%-8.24% (for chromium). In the analysis for checking the accuracy of the present method with some SRM′s,the analytical results obtained were in consistency with the certified values.