The aim of this study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for the determination of enriched species-specific mercury tracers at ng L^-1 levels (ppt) in zooplankton and aquatic samples from biological tracer experiments. Applying a cold vapor sector field ICPMS method a high sensitivity was obtained, i.e., 10⁶ cps for 1 μg L^-1 of natural mercury measured on ²⁰²Hg ⁺, which in turn enabled the measurement of mercury isotope ratios with a 0.6-1.4%R.S.D. precision for a 50 ng L^-1 standard. This method was used to quantify CH₃ ²⁰¹Hg⁺ and ²⁰⁰Hg²⁺ tracers in zooplankton from a biological tracer experiment with the aim of investigating the effects of algal density and zooplankton density on mercury bioaccumulation in zooplankton in a fresh water system. For quantification purposes a known amount of ¹⁹⁹Hg ⁺ was added to the zooplankton samples before digestion. The digested samples were analyzed and the resulting ICPMS spectra split into four spectra one for each of the four sources of mercury present in the sample (CH ₃ ²⁰¹Hg⁺, ²⁰⁰Hg²⁺, ¹⁹⁹Hg²⁺ and natural mercury) using algebraic de-convoluting. The CH₃ ²⁰¹Hg⁺ and ²⁰⁰Hg²⁺ tracers were quantified using an isotope dilution approach with the added ¹⁹⁹Hg⁺. Detection limits were 0.6 and 0.2 ng L^-1 for ²⁰⁰Hg⁺ and CH ₃ ²⁰¹Hg⁺, respectively. The coefficient of variation on the tracer determinations was approximately 18% CV estimated from the analysis of real samples with tracer concentrations in the <0.1-100 ng L^-1 range. The developed method was successfully applied for the determination of species-specific mercury tracers in zooplankton samples from a biological tracer experiment.