Male bisexuality does not exist, psychologists in the United States have claimed.
A new study concludes that the large majority of men purporting to be bisexual are actually gay whilst the rest are more likely to be heterosexual.
Senior author, Dr Michael Bailey, from Northwestern University in Chicago, said: "Bisexual male behaviour certainly exists but the study suggests that a bisexual orientation, an actual sexual preference for both men and women, does not exist in men.
"If such men exist, they are certainly very rare and we didn't find them." Researchers recruited 101 young adult men, 33 identifying themselves as bisexual, 30 straight and 38 homosexual.
They were questioned at length about their sexuality before before being seated alone in a laboratory to watch erotic films while their arousal levels were monitored by a sensor. Gay men were aroused by images of men and heterosexual men, by women.
But psychologists said those claiming to be bisexual were only aroused by one or the other - 75 per cent by men and the rest by women. Dr Bailey acknowledged that the study would certainly raise the ire of many men within the gay community, but said he stood by the science.
By way of explanation, he suggested that some may claim to be bisexual as it is easier than admitting to being gay whilst others might consider it some kind of achievement and be proud to swing both ways.
The study is to be published in the journal Psychological Science.