  Three kinds of magnetic resonance signals were detected in crystals of the
spin-gap magnet TlCuCl_3.
  First, we have observed the microwave absorption due to the excitation of the
transitions between the singlet ground state and the excited triplet states.
This mode has the linear frequency-field dependence corresponding to the
previously known value of the zero-field spin-gap of 156 GHz and to the closing
of spin-gap at the magnetic field H_c of about 50 kOe.
  Second, the thermally activated resonance absorption due to the transitions
between the spin sublevels of the triplet excitations was found. These
sublevels are split by the crystal field and external magnetic field.
  Finally, we have observed antiferromagnetic resonance absorption in the
field-induced antiferromagnetic phase above the critical field H_c. This
resonance frequency is strongly anisotropic with respect to the direction of
the magnetic field.
