Actress Kirstie Alley has hit back at reports that her friend John Travolta is gay.

Alley, 61, told US news anchor Barbara Walters on Wednesday that rumours about Travolta being homosexual were completely unfounded.

"I know John with all my heart and soul; he's not gay," she said.

"I think in some weird way, in Hollywood, if someone gets big enough and famous enough, and they're not out doing drugs and they're not womanising, what do you say about them?"

Alley told Walters that she fell madly in love with Travolta on the set of their 1989 movie Look Who's Talking.

She said Travolta was the greatest love of her life.

"Believe me, it took everything that I had, inside, outside, whatever, to not run off and marry John and be with John for the rest of my life," Alley said.

The actress said she had a major crush on the late Patrick Swayze, but did nothing about it because she knew how much he loved his wife.