Consider a second order
degenerate parabolic operator L. The present paper is concerned with the uniqueness
of solutions of the Cauchy problem: Lu = f in a strip 0 < t ≦ T, u(0,x) = ϕ(x) for all
x in Rn. It is proved that there is at most one solution subject to a growth condition
which depends on the degeneracy of L. In the special case where L is ultraparabolic,
uniqueness is proved under only onesided growth condition. The methods used
involve the construction of comparison functions in suitable sequences of
domains.