HYPERFINE EFFECTS AND LARGE 1 M(2)Q CORRECTIONS/

Effects associated with hyperfine mass splitting between pseudoscalar and vector mesons may induce surprisingly large 1/m(Q)2 corrections in the heavy quark expansion. We demonstrate this in a relativistic quar k model by calculating to all orders in 1/m(Q), with and without hyper fine effects, and comparing to the first order results. Total correcti ons of 30% or more are quite possible in the decay rates for B --> Dln u and B --> Dlnu near zero recoil.