The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil(-1) was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil(-1) and within 5 days when 0.003 g kg soil(-1) was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil(-1) was eliminated within 2 days by 1 g biomass kg soil(-1) and within 25 days when 0.01 g biomass kg soil(-1) was used. In unsaturated soil, about 60% [U-ring-C-14]atrazine was converted to (CO2)-C-14 within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after a starvation period of 240 days : 15 mg newly added atrazine kg soil was eliminated within 5 days.