Abstract:Following treatment with cibenzoline, a new antiarrhythmic agent, 23 of 53 patients showed positive proteinuria reactions. In all cases, these results were obtained with bromphenol reagent strips. Subsequent exposure of serial dilutions of cibenzoline to these reagent strips showed positive protein reactions at concentrations as low as 1 mg/ml. Treatment of these same solutions with acetic acid‐sodium acetate heat coagulation technique produced negative findings. Specimens from 14 of the above patients were then retested employing both techniques, and in all cases the reagent strips produced positive results while the heat coagulation technique (or sulfosalicylic acid) produced negative results. Therefore, it appears that cibenzoline produces false‐positive proteinuria results when bromphenol reagent strips are employed for analy