The Hasse principle for similarity of hermitian forms

The Hasse principle for similarity is established for restricted classes of skew-hermitian forms over quaternion division algebras with canonical involution and for hermitian forms over division algebras with involution of the second kind. A counterexample is produced to show that the principle cannot hold for skew-hermitian forms over quaternion division algebras in general. This settles the two final cases of Hasse principles for similarity of forms that were missing in the literature. (C) 2004 Elsevier Inc. All rights reserved.