Using the theory of spectral
subspaces associated with a group of isometries of a Banach space it is proved that
each derivation of an AW∗-algebra is inner. This constructive method of proof yields
a generator b for the case of a skewadjoint derivation which is seen to be the unique
positive generator such that ∥bp∥ = ∥δ|Ap∥ for each central projection p in the
AW∗-algebra A.