Hendrik Hertzberg writes that the end of the Cold War and the coming of global warming have brought about increased support for nuclear power, even among some environmentalists (The Talk of the Town, March 22nd). But many of us who work on nuclear-proliferation issues are dismayed by the growth of nuclear energy. Expanded nuclear power in industrial countries will inevitably mean expanded nuclear exports to less developed countries as manufacturers try to recoup their investments in a limited domestic market by selling abroad. It can be shown statistically that countries that receive nuclear assistance are more likely to build nuclear weapons, especially when they perceive threats to their security. India, Pakistan, and Israel started their nuclear programs with the importation of research reactors carrying peaceful-use requirements; with help from other countries, they were able to then realize their desire for weapons. Iran appears to be heading in the same direction. Given the documented interest in nuclear materials of terrorist organizations like Al Qaeda, and given the questionable assumptions that nuclear-energy economics is fraught with, it makes little sense to push nuclear power at a time when protections against proliferation are still so problematic. Improved energy efficiency is a safer, greener, and cheaper alternative.