A laboratory procedure using an artificial soil (“Artificial Soil Test”) and Eisenia fetida as test species is widely used to investigate the toxicity of pesticides to earthworms. In order to validate the results of this test in respect to natural earthworm populations, and to allow the ecological significance of the laboratory data to be interpreted and extrapolated to the field, a field test was developed. Pesticides were sprayed on perennial grassland plots which had high abundances and species diversities of earthworms. In the field tests, the biomass of the earthworms and their abundance were determined shortly (4–6 weeks) after pesticide application in spring, in autumn of the same year, and in spring of the following year. To date, 21 field tests using 12 different products have been conducted. The pesticides were sprayed at the highest recommended application rate and at four times this rate. An exposure calculation was used which allowed comparison of laboratory LC₅₀-values to “estimated environmental concentrations” (EEC) in soils derived from field application rates. A good correlation was found between laboratory results and effects on earthworm populations in the field. Relatively pronounced field effects were observed with pesticides of high intrinsic toxicity and high application rates; short-term effects were found with the less toxic compounds. No, or negligible, effects were found on earthworm populations in the field with pesticides that showed low toxicity to earthworms in laboratory tests, or that were applied at low rates.