Parties were held last week to celebrate the 64th birthday of North Korean leader Kim Jong-il — even in Japan, which has a troubled history with its near-neighbour. In Tokyo, the General Association of Korean Residents in Japan, which mainly comprises ancestors of Koreans who were forcibly taken to Japan during its 35-year occupation of the Korean Peninsula, held a party to mark the occasion. And those who attended were able to toast a recent diplomatic victory over Japan, in which the North Korean government was, incredibly, allowed to claim for itself the mantle of scientific objectivity.

The victory concerns the status of DNA tests conducted in Japan in 2004 on human remains that had been passed on from North Korea to Japan. North Korea said the remains were those of Megumi Yokota, a Japanese citizen that North Korea has admitted to kidnapping in 1977. Based on the DNA tests, however, Japan insists that the remains are those of someone else, and continues to demand an account of what really happened to Yokota.

But last January, in an interview with Nature, the scientist who carried out the DNA tests admitted that they were not conclusive (see Nature 433, 445; 2005). He has since been prevented from giving a full and open account of the matter.

Japan now needs to either produce some evidence to back up its claims that the DNA tests were conclusive, or admit that they weren't.

Japan now needs to either produce evidence to back up its previous claims that the DNA tests were conclusive, or admit they weren't, perhaps as a result of a lack of DNA in the incinerated remains.

But admitting such an error is something to which Japanese officials are inherently adverse. They may fear losing face — but such a loss would only be temporary, and coming clean would strengthen Japan's position in the longer term. There would still be no solid evidence to support North Korea's claim that Yokota was cremated. Japan could then continue to press North Korea for a plausible account of what really happened to Yokota and many other kidnapped Japanese nationals.

Instead, as things stand, the issue of the DNA tests on the bones has presented Japan with a thorny diplomatic problem. And the North Koreans are taking full advantage.

At bilateral talks two weeks ago, North Korea invited Japan to arrange a joint meeting of researchers to discuss the DNA analysis. Japan declined the offer, continuing to insist that its original interpretation was correct. This left the guests at Kim's birthday party gleefully dancing on their firm scientific ground: “We just want the truth to come out,” they gloated. “We want to proceed scientifically.”

Japanese officials need to learn from their mistake. In jostling with Kim's unpleasant regime, they need to be sure to retain the moral high ground. Public statements based on the wrongful interpretation of scientific data are liable to backfire. Refusing to acknowledge such problems at the first available opportunity tends to compound them, resulting not just in a loss of face, but of credibility.