  We present the coefficient of the chromomagnetic interaction operator, the
only unknown coefficient in the Heavy Quark Effective Theory (HQET) lagrangian
up to the $1/m$ level, with the two-loop accuracy by matching scattering
amplitudes of an on-shell heavy quark in an external field in full QCD and
HQET, and obtain the two-loop anomalous dimension of this operator in HQET.
