High levels of testosterone might make men more trustworthy, a study has found.
The male hormone, which boosts libido and builds muscle, is often associated with aggression and anti-social behaviour.
But testosterone-fuelled hunks may also be less likely to lie and cheat than some of their brothers, the research suggests.
Scientists boosted the testosterone levels of 46 men by smearing their skin with a gel containing the hormone.
Another 45 men were treated with a 'dummy' placebo gel lacking any testosterone.
Both groups were then asked to take part in a behavioural study which involved playing a simple game of dice in an isolated booth.
The higher the scores they entered into a computer, the more money they received as a reward.
Neuroscientist Professor Bernd Weber, from the University of Bonn in Germany, said: 'These experiments were designed such that the test subjects were able to lie.
'Due to the separate booths, nobody knew whether they were entering their real scores into the computer, or higher ones in order to get more money.'
However, the scientists were later able to determine if any of the volunteers had been cheating.
The results, reported in the online journal Public Library of Science ONE, showed that men with boosted testosterone lied less.
'Test subjects with the higher testosterone levels had clearly lied less frequently than untreated test subjects,' said co-author Professor Armin Falk, an economist also from the University of Bonn.
'This result clearly contradicts the one-dimensional approach that testosterone results in anti-social behaviour.'
The hormone was likely to increase a man's sense of pride and the need to develop a positive self-image, he said.
'Against this background, a few euros are obviously not a sufficient incentive to jeopardise one's feeling of self-worth,' said Prof Falk.