The detection of small frontal and high-parietal subdural effusions by ultrasound examination has some problems of methods. The diagnostic accuracy of the noninvasive investigation may be improved by using the following proceeding. The application of a short-focus transducer (focus-zone 1 to 4 cm) instead of the usual medium-focus transducer; The noninvasive measurement of intracranial pressure by aplanation-tonometry of the fontanelle. We report our results with this proceeding in 35 infants with liquid accumulation between cortex and cranium (27 infants with subdural effusions, 8 infants with enlarged subarachnoid spaces because of brain atrophy). The ultrasound features of a flattened superficial relief of brain-cortex and a wedge-shaped enlarged interhemispheric fissure are morphologic references to subdural effusions. Strong reflexions of the convexly arched superficial relief of brain-cortex, an enlarged interhemisphaeric fissure with parallel vertical bounds and enlarged lateral ventricles in the frontal parts with irregular outlines are signs for brain atrophy with enlarged subarachnoid spaces. If sonographic signs do not allow an accurate diagnosis, the noninvasive measurement of intracranial pressure bei aplanation-tonometry enables us to discriminate between subdural effusion and enlarged subarachnoid spaces by measuring a rised basic pressure and pathologic pressure waves (results from 26 long-term measurements in the above-mentioned 35 infants).