The paper outlines a method for determining pirimiphos-methyl on tomatoes and tomato leaves as well as in the soil by gas-chromatography with the lowest detectable level of 20.10(-12) g. By means of this method after cold fogging application of 0.25 ml Actellic 50 EC.m-2 in a greenhouse initial residues of 0.04-0.38 mg.kg-1, and after 4 days of 0.04-0.25 mg.kg-1 were found. These results are below the maximum residue limit of 0.4 mg.kg-1 for pirimiphos-methyl in tomatoes after 4 days. For determination of the decrease of the agent on various surfaces residue-life 50% was calculated. It was found to be 0.66 days for the surfaces of leaves, 0.56 days for the surfaces of glass with light, and 0.69 days for glass with darkness. On soil surfaces under the same conditions the decrease is much lower with a residue-life 50% of 7.1 or 12 days, respectively.