The ground-state hyperfine splitting values of high-Z hydrogenlike ion
s are calculated. The relativistic, nuclear, and QED corrections are t
aken into account. The nuclear magnetization distribution correction (
the Bohr-Weisskopf effect) is evaluated within the single-particle mod
el with the gs factor chosen to yield the observed nuclear moment. An
additional contribution caused by the nuclear-spin-orbit interaction i
s included in the calculation of the Bohr-Weisskopf effect. It is foun
d that the theoretical value of the wavelength of the transition betwe
en the hyperfine-splitting components in Ho-165(66+) is in good agreem
ent with experiment.