A rapid screening method for β-agonists in cattle urine was developed that offers speed and protocol simplicity and that could be performed on the spot. The method consists of an extraction on Empore membranes with strong cation exchange properties and a test strip immunoassay. The Empore extraction provides a fast and simple cleanup of the urines and a concentration step with recoveries ranging from 50-80% for the β-agonists of the aniline type and around 10% for salbutamol and terbutaline. A test strip immunoassay is performed on the diluted extract. With the use of an antiperoxidase antibody, an internal negative control was included, to which all color reductions are compared. Although a portable colorimeter increased the sensitivity of the test, a visual interpretation was sufficient to give a correct yes/no answer. The whole test takes about 30 min and has a visual detection limit for clenbuterol of 1 ng/mL of urine. The test also shows good sensitivity for salbutamol, despite the low recovery with the Empore extraction.