The results of seven case studies by the author, colleagues, and graduate students performed at contaminated sites indicate that monitoring wells and piezometers installed in karstic carbonate aquifers often yield unreliable data. These devices more often gave misleading than useful information concerning aquifer properties, groundwater flow, and contaminant movement. These findings are in accord with the highly anisotropic and heterogeneous nature of these aquifers. The following cautions are provided when monitoring wells are to be used in karstic carbonate regions. (1) Monitoring wells may be unreliable in detecting contaminant releases. (2) A monitoring well that detects a contaminant is unlikely...