The influence of four pesticides, e.g. glyphosate, paraquat, atrazine, and carbaryl, on the activities of invertase, urease and phosphatase of twenty-two soils, numbered as 1-22, was investigated. Soils displayed a general variability of enzyme activities with invertase being more abundant than urease and phosphatase in the order listed. The addition of glyphosate and paraquat activated invertase and urease activities in several soils. Increments of invertase activity ranged from a very low increase (+4%) up to +204% in soils 11 and 14, respectively. Smaller increases were measured for urease. A general inhibitory effect (from 5% to 98%) was observed for phosphatase in the presence of glyphosate. The effects of atrazine and carbaryl on the three soil enzymes were evaluated against that exhibited by methanol, the solvent used for their solubilization. In almost all soils, atrazine further inhibited invertase activity with respect to the inhibitory effect shown by methanol. By contrast, consistent activation effects (from 61% to 10217%) were measured for urease with methanol alone and/or methanol-pesticide mixtures. Contradictory results were observed with phosphatase. Similarities found between the results obtained with enzymes in soils and those measured with synthetic enzyme complexes (e.g. free enzymes and/or clay-, organo-, and organo-clay-enzyme complexes) exposed to the same pesticides allowed some relationships between responses of soil enzymes to pesticides and soil properties to be hypothesized.