Are there quasistable hadrons containing superheavy quarks?

Flavor-changing neutral currents are reconsidered allowing the possibility that superheavy quarks, with masses comparable to the weak-boson mass, exist in nature. It is argued that the natural conservation of these weak neutral currents cannot be imposed to order αGF in this case. Rather, the absence of strangeness-changing (and possibly charm-changing) neutral currents to this order suggests that the mixing angles between ordinary and superheavy quarks must be extremely small. Some phenomenological ramifications of this restriction are presented.