A novel and rapid approach to quantify chloride concentration in sweat for early detection of cystic fibrosis (CF) is shown in this work. Disposable screen-printed sensor (SPS) devices capable to induce sweat and measure the chloride concentration are presented. Pilocarpine, which was forced into de skin by means of iontophoresis, has been used to stimulate the sweat glands. Chloride concentration has been directly measured on the skin by potentiometry. The performance of the devices has been tested in synthetic samples, obtaining good agreement with the Nernst equation. Sensors reproducibility has been analyzed in terms of residual standard deviation (RSD), obtaining a value of 8% (n=6 and alpha=0.05). Finally, the application of these sensors in several volunteers has been carried out. The results were compared with the method generally used in hospitals, obtaining deviations minor than 8%.