  We consider the Johnson-Koranyi-Hua system on symmetric Siegel domains of
type two. We prove that all functions which are annihilated by the system and
satisfy an H^2 integrability condition are pluriharmonic. So the situation is
completely different on type two domains than on tube type domains: it was
proved by Johnson and Koranyi that on symmetric tube type domains the system
characterizes Poisson-Szego integrals.
