The HD functionality allows LoveFilm Instant members to stream selected films and TV shows over the internet in HDTV resolutions up to 1080p for no extra charge.
LoveFilm Instant, the streaming-only package launched last year, on PC or Mac will give the option for full 1080p high definition, but members using their Xbox 360 or Samsung and LG connected TVs will get only 720p resolution.
In the UK, HD streaming titles now available include The Twilight Saga: Eclipse, Gnomeo and Juliet and Four Lions, along with US TV shows such as Lost and Ghost Whisperer, and BBC documentaries, including Human Planet and Planet Earth.
LoveFilm said that more HD titles would be added to the service over the "coming months".
"LoveFilm is the number one consumer choice for subscription film and TV series streaming in Europe," said Jim Buckle, who became the managing director of LoveFilm following the departure of Simon Calver.
"The introduction of HD quality content further strengthens the offering and marks another key milestone in delivering our members the best possible service with exceptional value."
LoveFilm feels that the addition of HD streaming "strengthens its offering" to subscribers, but it also provides a strong selling point in the battle with rival Netflix.
However, customers are warned that they will need a minimum internet connection of 4mbps for the 720p streaming, while the full 1080p content requires 12mbps or higher.
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