Britney Spears = Ratings for Glee

Britney Spears apparently is still popular and moves the meter.

Tuesday's episode that featured the star in some dream-sequence cameos drew an estimated 13.5 million viewers. The Nielsen Co. says it was the second most-watched episode of the show ever, behind last spring's return from a hiatus.

That's also an increase from the 11.1 million people who had tuned in to the "Glee" season premiere a week earlier. Spears was also a trending topic on Twitter during the telecast, exemplifying one of TV's biggest new trends: viewers using social media to correspond with friends while watching.

The show's cast performed five Spears songs during the episode, including "I'm a Slave 4U" and "Stronger."