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 ..cap alpha..G/sub F/ 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.