  Given a central simple algebra with involution over an arbitrary field,
\'etale subalgebras contained in the space of symmetric elements are
investigated. The method emphasizes the similarities between the various types
of involutions and privileges a unified treatment for all characteristics
whenever possible. As a consequence a conceptual proof of a theorem of Rowen is
obtained, which asserts that every division algebra of exponent two and degree
eight contains a maximal subfield that is a triquadratic extension of the
centre.
