  With the advent of large-collecting-area instruments, the number of objects
that can be reached by optical long-baseline interferometry is steadily
increasing. We present here a few results on massive binary stars, showing the
interest of using this technique for studying the insight of interactions in
these systems. Indeed, many massive stars with extended environments host, or
are suspected to host, companion stars. These companions could have an
important role in shaping the circumstellar environment of the system. These
examples provide a view in which binarity could be an ingredient, among many
others, for the activity of these stars.
