Bacterial strains were isolated from different scale wastewater treatment plants with different sewage loads. Both Pseudomonas isolates differ significantly in their decolourization potential. Fluorone dyes (erythrosine and Bengal rose) were almost two times better removed by strain SDz3 (Table 1) isolated from large-scale wastewater treatment plant in Katowice (80 % and more regardless of dyes concentration). For both strains, increase of erythrosine concentration caused decrease of decolourization and at the same time, Bengal rose was more effectively removed in samples with higher concentration.