Proftest SYKE carried out the proficiency test in cooperation with the KVVY Tutkimus Oy for the laboratories conducting leaching tests for solid waste samples at the turn of the year 2017-2018. The results of the up-flow percolation test (EN 14405:2017) for fly ash samples were compared and evaluated. In total, 8 participants joined in the proficiency test. Either the mean or the median of the results reported by the participants was used as the assigned value for the measurands. The overall performance evaluation was done with the En scores and 64 % of the all the evaluated results were satisfactory. The performance evaluation for the results for pH as well as for the cumulative values L/S 2 and L/S 10 of the measurands was done also with the z scores. In the evaluation based on z scores, 85 % of the results were satisfactory, when deviation was set to 0.5 pH units, to 20 % for SO4 and to 50 % for other measurands. For these same results, 78 % of the results were satisfactory when evaluated with the En scores. Warm thanks to all the participants!