  A problem, whether a neutrino-antineutrino transition could be responsible
for the muon neutrino deficit found in underground experiments
(Super-Kamiokande, MACRO, Soudan 2) and in the accelerator long-baseline K2K
experiment, is discussed in this paper. The intention of the work is not
consideration of concrete models for muon neutrino-antineutrino transition but
a desire to attract an attention to another possibility of understanding the
nature of the measured muon neutrino deficit in neutrino experiments.
