The application of formalin to the ground is a commonly used method to estimate the abundance and biomass of earthworms in soil. From April to September 2003, we investigated potential negative side effects of this method on soil organisms and plants in the sampling soil area to which formalin has been applied. The application of 0.4% formalin (40 L per 0.25 m(2)) severely decreased abundances of Collembola and Nematoda, soil respiration, dehydrogenase activity, fatty acid contents, vegetation cover, and shoot and root biomass. These effects lasted for the whole study period. The impact of formalin may have been aggravated due to unusually hot and dry weather conditions. However, owing to its harmful consequences, the formalin method cannot be recommended as a standard for earthworm extraction.