Japan might be famous for its flash in the pan fads, but amid the welter of new crazes, there is one that endures: blood groups. Almost the first question on the lips of Japanese teenagers is "What is your blood group?"

But the matter is also taken seriously by adults: companies have planned departments around the blood types of their workers, and a baseball coach is even said to have used it in selecting his teams.

The heart of the matter

At Tokyo's Zelm dating agency, the culmination of the evening is a party directed by a rather dictatorial hostess. Ten hopefuls of each sex spend at least an hour in small cubicles, each with a computer that links them up. They ask all sorts of questions about each other, many fairly intimate.

But top of the list of important features in their potential partners is blood type.

"I like 'O' because 'O' is very understanding," explained Masako Mishinami.

"Group 'A' can get very nervous easily - they're very narrow minded. But 'O' is very open and friendly - and 'B' is very attractive and strong, but doesn't listen to your opinion."

Meanwhile, a gentlemen whose name I didn't dare ask, was having a rough time romantically. The reason, of course, was blood groups.

"My real problem is that I adore 'A/B' girls, but there are very few of them in Japan," he said.

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But blood groups in Japan reach well beyond the question of romance. During World War II, Japan's Imperial Army is rumoured to have formed battle groups according to blood type.

Many base their political analysis on it. One man told me Japan had done so well since the war, because the majority of prime ministers were type 'O' ... as for Hashimoto... well he's an 'A/B' ...so no wonder things are sliding.

Blood on the Web

But why stop at politics. One of Japan's most active Websites for blood groups is run by Mr Shinoki. He believes blood groups could shape the future of the world, by promoting international understanding.

"I expect blood group observation and interest in blood types will one day form a global network. And one day we human beings will start to make friends through the question: 'What is your blood type?' And I believe it will be a really useful means of getting to know each other and communicating."

A burgeoning industry

It goes without saying that an industry has grown up around blood groups. You can buy blood type chewing gum, soft drinks, calendars, and - surprise, surprise - blood group condoms.

The marketing of these condoms, is rigorously thought out at the office of Jex condoms - the third largest manufacturer in Japan.

Ten percent of their products are based on blood type, with packaging geared to the blood group of the intended user - I wasn't sure if it was the man's or the woman's.

But the director of Jex condoms, Kinya Kawasaki, insists that doesn't matter. He says his customers tell him that believing condoms are specially made to suit something as important as one's blood group, makes sex just that little bit more special.