Abstract. We give necessary and sufficient conditions for a tuple of unbounded operators to be (jointly) subnormal. This criterion is then applied to characterize the subnormality of some special tuples of operators, in particular commuting bilateral weighted multi-shifts.

AMS Subject Classification (1991): 47B20, 44A60, 47A20, 47B37

Received February 11, 2002, and in revised form May 10, 2002. (Registered under 2930/2009.)