A charity has called for bike helmets to be included in London's cycle hire scheme after it emerged six people had been injured since it began.
Some 750,000 journeys have been made since the scheme's launch in July.
But the bikes do not come with helmets - and at least one person has been taken to hospital for head injuries in that time.
Road safety charity Brake said helmets were "imperative". But Transport for London (TfL) said accidents were low.
A Brake spokeswoman said: "We recommend all adult cyclists wear one, as well as children, whether you are cycling on or off road.
"Schemes like the cycle hire project are great but some kind of helmet is surely imperative when users have to travel on such busy roads.
"It must be looked at."
She added: "Wearing a helmet consequently can prevent some fatal or serious brain injuries."
A TfL spokesman said: "There have been six incidents where a cycle hire user has been injured since the scheme launched on July 30.
"This should be seen in the context of the 750,000-plus cycle journeys that have been made on the hire bikes to date."
He continued: "The use of cycle helmets is not a legal requirement.
"In addition, for a helmet to be effective it has to be the appropriate size and fitted properly."