  We show that the bilinear complexity of multiplication in a non-split
quaternion algebra over a field of characteristic distinct from 2 is 8. This
question is motivated by the problem of characterising algebras of almost
minimal rank studied by Blaeser and de Voltaire in [1].
  This paper is a translation of a report submitted by the author to the XI
international seminar "Discrete mathematics and applications" (in Russian).
