Scientists in India and Pakistan have reacted indignantly to the discovery that some of their collaborations with international partners may be coming to an abrupt end. This is a result of sanctions imposed by the United States and others in the aftermath of the nuclear weapons tests conducted by both nations in May. They are entitled to be upset. But they can hardly be surprised. After all, international non-proliferation efforts that have sought with some success to restrict the spread of nuclear weapons are based on the concept that defiance should be punished. It is hard to see how such efforts can maintain any credibility if no punishment is now forthcoming.

Despite India's protestations (see page 513), the Western response so far has been relatively limited. The US government is only withdrawing funds from collaborations with agencies directly involved in the nuclear weapons and ballistic missiles programmes of both countries (India is the chief target, as such work had already ended under earlier economic sanctions against Pakistan). In some cases, the target of such sanctions is legitimate. But these agencies are also involved in many branches of research that have nothing to do with nuclear weapons or missiles.

The human cost of such actions can be considerable, even if they do not mark the end of scientific collaboration between the United States and the sub-continent. The State Department is showing some discretion; the law that automatically triggered sanctions when the Indian tests took place could be interpreted more harshly, requiring an end to all US-supported scientific collaboration. Amid allegations of a clamp-down on all scientists from the sub-continent seeking visas to travel to the United States, the State Department says that it is working out a new policy on the circumstances in which these can be issued.

As they do so, however, department officials should ask themselves who benefits from the curtailment of scientific contact or collaboration between India and Pakistan and the West. Such curtailment will do little to slow down the clandestine weapons programme of either country. But it will worsen the isolation of both at a time when greater engagement with the outside world is the best available hedge against a potentially cataclysmic military confrontation between them. Indeed the clearest beneficiary, perhaps, is the nationalist government of India, which started the whole crisis in the first place and would reap crude political gains from any moves to isolate Indian science and marginalize its scientists.

This contradiction affects not only scientific sanctions but all the others which the United States has put in place. The imposition of sanctions by the world's largest economy on the world's largest democracy was always likely to expose the limitations of such a strategy as an instrument of foreign policy. Indeed the US Congress has already admitted as much, exempting massive grain sales from the sanctions in order to please American farmers. The realization that the most economically significant sanctions cannot survive poses a new danger: that effective sanctions will be allowed to lapse, leaving in place a series of token measures, of which the restriction of scientific collaboration could well be one. That would be a ridiculous outcome.

Scientific collaboration between the Indian subcontinent and the West is an essential line of communication that both sides must now fight to preserve. At the very least, the National Academy of Sciences and the US scientific societies should press the State Department to maintain normal scientific relations as far as is possible within the letter of the sanctions law and, in particular, to maintain the right of scientists from the two countries to travel freely. Even non-proliferation efforts would benefit.