Knight Frank is rejoining Zoopla on a trial basis after leaving five years ago when it helped set up OnTheMarket.
The trial consists of 21 London offices listing for a three-month period.
However, Knight Frank has expressed its ongoing commitment to OTM.
Knight Frank, along with Savills, Strutt & Parker, Douglas & Gordon and Chestertons, was a founding member of OTM.
At the time, it had a ‘one other portal’ rule which required agents listing with OTM to list on only one other portal – effectively forcing a choice between Zoopla and Rightmove.
All the founding agents apart from Savills have now returned to Zoopla, although Savills does list its overseas properties on Zoopla.
A spokesperson for Knight Frank said: “We remain committed investors in OnTheMarket and are strong supporters of it as the agent-backed portal.
“Last year we signed a five-year strategic agreement to display all our sale and lettings properties at OnTheMarket and we see it going from strength to strength.
“We are constantly assessing the changing marketing opportunities for our clients.”