  The absence or presence of extremely wide binaries with a radio pulsar and an
optical counterpart imposes a strong constraint on the existence and magnitude
of kicks in supernova explosions. We search for such systems by comparing the
positions of radio pulsars which are not known to be in binaries with the
positions of visible stars, and find that the number of associations is
negligible. According to the performed population synthesis, this implies that
kicks must occur, with a lower limit of at least 10 to 20 km/s.
