Studies on 52 patients show the value of loading tests (drinking test, homatropine-load, coffein-trial and cervical vein compression) in complicated heterochromia (Fuchs). In 216 tests, the wastage was 5.1 percent in the controls and 14.5 percent with pathological eyes. The drinking-test was the most sensitive (approximately 10 percent), but in a few cases a pathological rise of pressure was obtained with the other tests. Therefore the performance of loading tests in congenital heterochromia (Fuchs) is indicated in diagnosis and treatment.