The belief that geopathogenic zones exist and could cause morbidity is widespread. It is increasing even among physicians. Presently, in health care it is going to even gain an economical dimension by causing investment costs for claimed protective means and by influencing hospital planning, design and management. Therefore, this issue is no longer just a private borderline issue but has become publicly relevant. In view of the fact that relevant studies are lacking, it deserves scientific clarification. In a double-blind study this hypothesis was tested by two different approaches: First, it was investigated whether location-bound biologic effects could be identified at all. To remain independent from dowsers, an investigation area of 35 m(2) was chosen which was large enough to ensure the presence of at least one postulated adverse zone. This area was scanned in 0.5 m intervals by monitoring bioparameters such as skin resistance, reaction time and heart rate variability in 43 volunteers. Skeptics were excluded. Location-dependent changes were investigated by point-by point analysis of local data distributions and by analysing the two-dimensional spatial distributions of the measured bioparameters by cross-correlation analysis. In a second approach, 5 independent experienced dowsers were asked to locate geopathogenic zones within the area both to verify the adequate choice of the area and to correlate the pattern of dowser's scorings with the patterns of biosignal distributions. Neither of these approaches showed statistical significant differences. The investigation did not confirm the hypothesis that local geopathogenic zones existed and, hence, would need protective actions.