This article evaluates a recently developed qualitative sweat patch test (SPT). A battery-powered stimulator with polymer pad electrodes is used to stimulate sweating, followed by the application of a paper patch which collects the sweat and shows color change on sweat chloride levels above 40 to 50 mEq/l. Our data consist of 66 patients with cystic fibrosis, 75 control subjects, and 37 relatives of patients with cystic fibrosis, excluding 22 subjects (11%) with insufficient sweat. There were no false-negative results among 66 patients with cystic fibrosis, and in the control group, 71 of 75 subjects gave negative results and the other four gave positive results. Of the 37 relatives, eight gave positive results; all of the eight subjects are parents of patients with cystic fibrosis. Our results indicate that SPT is useful and reliable when there is sufficient sweat. This portable and simple patch test may serve as an excellent screening test for cystic fibrosis.