Pharmacokinetic studies in broilers and layers of different sulphonamides indicate a good absorption and a long elimination half‐life (of sulphaquinoxaline, sulphadimidine and to a lesser degree sulphadiazine) resulting in high plasma concentrations during drinking water medication in the recommended therapeutic doses. In contrast drinking water medication with high concentrations of trimethoprim (up to 1.320 mg/liter) resulted in a maximal mean plasma concentration of 1.2 μg/ml.