ABSTRACT: The transmissivity coefficient (T; measured in m2·s-1) is one of the most important resistivity characteristics of aquifers. In terms of assessing the importance of aquifers for water supply purposes, the transmissivity coefficient is the most significant and mutually best comparable hydraulic parameter which completely characterizes aquifer transmissivity. The methodology of evaluating regional Slovakian hydraulic parameters was implemented many years ago. This process delivered the coefficient of transmissivity for regional prognosis from archival data and also from tests where only data on wells’ specific yield remains available. The basic requirement for calculating T from specific yield data is to have a true value of T which allows construction of the drawdown-over-time dependence graph. This paper highlights possible misinterpretations of hydrodynamic test results in transmissivity coefficient calculations performed in the rock environment of neovolcanic mountains in Central Slovakia.