A new Czech leaching test under the enactment No. 338/1997 was used to assess leachability of selected inorganic contaminants, in particular heavy metals, from fly ashes. Main analytical performance characteristics of the test (repeatability and reproducibility) were determined in a collaborative study using a procedure described in the standard ISO 5725-2. Ten laboratories from the Czech Republic participated in the study. The repeatability expressed as relative standard deviation of the leaching test ranged from ca. 1 % for macrocomponents to ca. 46 % for microcomponents, whereas the reproducibility ranged from ca. 6 % for macrocomponents to ca. 46 % for microcomponents.