  If the Theta^+(1540) is interpreted as a bound state of a $\bar s$ quark and
two (ud) diquarks in a relative P-wave, then it is very likely that there exist
pentaquark states with a heavy antiquark, $\bar b$ or $\bar c$, and two
``light'' diquarks in a relative S-wave which are stable against strong decays.
We make a mass estimate for exotic states of this type and discuss their weak
decays. Isospin relations are constructed which test their flavor quantum
numbers.
