The results of ammonia determination in urine with an electrode method as well as with a direct method were strongly correlated (r = 0.998), the electrode method yielding somewhat lower values (p < 0.001). The electrode method is simple. It requires 20 ml of urine of a pH not exceeding 7. Correction of the potassium error is necessary, thus a nomogram is presented. The direct method is simple in skilled hands, it requires 1 μl of urine. Presumably it provides the exact urinary ammonia concentration. Calculation of urinary potassium by performing both ammonia methods on urine samples showed a close correlation (r = 0.926) to measured urinary potassium.