The results of studying temperature behavior of the microwave surface imped
ance Z(s)(T) and conductivity tensor sigma (T) of high-T-c superconducting
(HTSC) single crystals are analyzed. The emphasis is on the experimental fa
cts that are inconsistent with the known electrodynamic concepts of conduct
ivity mechanisms in these materials. Possible reasons for the inconsistency
are discussed in the context of structural features of the HTSC crystals,
and the outlook for future investigations is outlined. (C) 2000 MAIK "Nauka
/ Interperiodica".