  We present a quantitative estimate of the anisotropic power and scaling of
magnetic field fluctuations in inertial range magnetohydrodynamic turbulence,
using a novel wavelet technique applied to spacecraft measurements in the solar
wind. We show for the first time that, when the local magnetic field direction
is parallel to the flow, the spacecraft-frame spectrum has a spectral index
near 2. This can be interpreted as the signature of a population of
fluctuations in field-parallel wavenumbers with a $k_{\parallel}^{-2}$ spectrum
but is also consistent with the presence of a "critical balance" style
turbulent cascade. We also find, in common with previous studies, that most of
the power is contained in wavevectors at large angles to the local magnetic
field and that this component of the turbulence has a spectral index of 5/3.
