Julia Roberts spent time with prostitutes before filming 'Pretty Woman'.

The 51-year-old actress shot to fame as sex worker Vivian Ward opposite Richard Gere as wealthy businessman Edward Lewis in the 1990 romantic comedy and spent time driving around Hollywood Boulevard with two women from the same background as her character as part of her research.

Barbara Marshall, a former nurse and the widow of the movie's director, Garry Marshall, has told how she was volunteering at a Los Angeles free clinic in 1989 when she got a call from her spouse.

She told the New York Post newspaper's Page Six column: ''Garry would never visit me at the clinic, because he was a hypochondriac and afraid of getting a disease. But he asked if Julia could come and talk to some of the patients.

''I recruited two young women who came to the clinic regularly, and I paid them $35 each to meet with Julia.

''I went back to work, and about 20 minutes later, Julia yelled from the end of the hall, 'Bye, Barbara. We're going to take a drive. We'll be back later.' ''

Barbara panicked and called her husband and told the director: ''Your star just left with a group of girls, and I think they were heading to Hollywood Boulevard. I'm worried. What if she doesn't come back?''

But the group returned later and Barbara praised Julia as ''one tough lady who can take care of herself on and off camera.''

And the ex-nurse was particularly proud of a scene where Vivian presents Edward with a selection of condoms and describes herself as a ''safety girl''.

She said: ''I was so proud, because I realised that Garry was paying attention to my work and respecting the importance of preventing sexually transmitted diseases.

''I will always be honoured that he was able to steal stories from my life and turn them into charming moments on film.''