Abstract The potential for biodegradation of s-triazine pesticides was investigated in laboratory batch and sequence batch experiments using a stable mixed bacterial community enriched on atrazine. The experiments were performed aerobically in a mineral salt solution complemented with a mixture of s-triazines as sole carbon and energy sources. Comparisons were made between the efficiency of the inoculum for atrazine degradation in mineral salt solution and in wastewater. In batch cultivation, atrazine, simazine, hydroxyatrazine, and terbutylazine were degraded to concentrations below 0.1 mg/liter after 6 days; evidence of the mineralization was the detection of 14CO 2from [U-ring- 14C] atrazine and the production of nitrate and chloride ions. The low degradation rate observed for cyanuric acid and desethylatrazine suggests that degradation proceeded via N-dealkylation and dechlorination. Nevertheless, degradation of ametryne and cyromazine presume the involvement of other degradation pathways. Evidence was given that presence of other additional carbon sources is not an obstacle to atrazine biodegradation, since better results were obtained using wastewater.