Gay male couples are significantly discriminated against on Airnbnb in Dublin.
A new study has found that they are 25% less likely to secure a booking in the capital, but lesbians are not.
The research, published in The Times, was carried out by Trinity economists who set up four separate accounts on the website for couples of varying sexuality.
The accounts were set up under the guise of two gay men, two gay women and a man and a woman.
Ronan Lyons and Rishi Ahuja also found that the level of discrimination was lower in more expensive areas of the city.
Some 600 identical messages were sent out across the different accounts.
The only difference in responses was the two gay men.
In an abstract describing the experiment, the authors say: "Online marketplaces were built with the implicit promise of reducing discrimination.
"Over time, though, online marketplaces have increasingly been designed to reduce anonymity as an exercise in trust building.
"While the reduction of anonymity can build trust, such design choices can also facilitate discrimination."
They say the study was the first to examine whether there is discrimination against those in same-sex relationships in the sharing economy.
The research found gay men were 20 to 30% less likely to secure a booking than identical guests in man-woman relationships.
Mr Lyons says the discrimination was not put in writing, but men were more likely to have their inquiry e-mail ignored.
"This difference is driven by non-responses from hosts, not outright rejection".
But he says male hosts, and those with many listings, are less likely to discriminate.
Discrimination against men in same-sex relationships was seen least in the most desirable locations.
"The findings are not consistent with taste-based discrimination but, with little evidence for statistical discrimination, they raise something of a puzzle about the underlying source of discrimination against those in (same-sex relationships)", the authors say.