To many Japanese, the key to their personality lies not in their stars but in their blood type. Type A's, they believe, are perfectionists and make good accountants; Type B's are sociable but selfish.
Now one of Japan's favorite pop beliefs is running into accusations of abuse and discrimination, with critics saying it is being used to assign jobs, match couples, even pigeonhole schoolchildren.
Irate scientists are attacking the theory in books and Web pages. Magazines are examining the debate in articles with titles like, "Don't bully Type B."
The debunkers point out that blood type is determined by the proteins in the blood _ hardly a determinant of character. "It's mere superstition," says Tatsuya Sato, associate professor of psychology at Ritsumeikan University. "Linking blood type and personality is not only unscientific, it's wrong."
Ryoichi Kikuchi of the Broadcasting Ethics and Program Improvement Organization, says his watchdog group has fielded hundreds of complaints.
"Viewers are now complaining about their children being bullied at school, couples breaking up and bosses treating underlings unfairly _ all because of blood type prejudice," he said.
Newspaper polls show only 20 percent of Japanese say they're convinced that blood type influences personality. But the theory, imported from its Nazi supporters and adopted by Tokyo's militarist government in the 1930s, is wildly popular nonetheless. It is also widespread in South Korea.
Blood type personality analysis appears regularly in Japanese women's magazines. Last year alone, more than 50 television shows dwelled on the subject. Matchmaking agencies offer blood type compatibility tests.
It is considered perfectly acceptable to ask a person's blood type and make it public. Blood types are listed in Japan's "Who's Who in Politics and Government." Prime Minister Junichiro Koizumi is an A, though his permed hair, in-your-face political style and fondness for pop music hardly fit the accountant stereotype.
Japanese television recently showed children at the Oi Nursery School in Saitama, just outside Tokyo, being divided into four groups according to blood type to compare how they eat snacks, clean garbage or take off their shoes at the door. The school declined a request for comment.
The theory has been around for decades, but its dark past is little known.
The discovery of blood types in 1901 was one of the greatest advances in medical history, but the breakthrough was then perverted by the Nazis to claim the superiority of Germans _ mostly types A and O _ over Jews, Asians and others with a larger proportion of type B blood.
The theory reached Japan in a 1927 psychologist's report, and the militarist government of the time commissioned a study aimed at breeding better soldiers.
The craze faded in the 1930s as its unscientific basis became evident. But it was revived in the 1970s with a book by Masahiko Nomi, an advocate and broadcaster with no medical background.
About 40 percent of Japanese are type A, 30 percent are O, 20 percent are B and 10 percent are AB. O's are said to be decisive and curious, while AB's are supposedly complex and suited for research and art.
The late Nomi's son, Toshikata, heads a private group called the Human Science ABO Center and stands by the theory. He says it's not intended to rank people and should be only used to make the best of one's talent and smooth out relationships.
"A, B and O blood classification is an effective, common indicator that can judge human beings regardless of race and religion," he said.
Sakumi Itabashi doesn't buy it. A liberal arts professor and author of "The Myth of Fortunetelling," he blames the craze on a national passion for efficiency and order.
"People want to find a rule in everything, including personality, because that makes things more predictable and they feel more secure," he said.
