  The concept of realism in quantum mechanics means that results of measurement
are caused by physical variables, hidden or observable. Local hidden variables
were proved unable to explain results of measurements on entangled particles
tested far away from one another. Then, some physicists embraced the idea of
nonlocal hidden variables. The present article proves that this idea is
problematic, that it runs into an impasse vis-\`a-vis the special relativity.
