Abstract In the 1970's the “Eötvös Lorand” Geophysical Institute performed Seismic reflection deep sounding experiments with multiple coverage in several parts of the Pannonian Basin (Posgay. 1975). One of the most interesting results was that arrivals were received in the time range corresponding to the depth of the asthenosphere. They were interpreted as reflections (Posgay et al., 1981). Conspicuous arrivals from the time range of the asthenosphere (15–20 s) were also received along the Pannonian Geotraverse in 1987. In the majority of sections published in other countries, the upper mantle seems to be transparent. The present paper discusses investigations and preliminary results, which lead to the conclusion that this apparent transparency is due to the frequency range below 10 Hz being neglected in both signal generation and recording in most deep continental reflection surveys. The Seismogeological conditions of the Pannonian Basin are certainly favourable for reflection studies of the upper mantle. The correctness of the assumption that arrivals from the time range of the asthenosphere are primary reflections is subjected to further investigation and conclusions are made concerning the structure of the asthenosphere.