From a magazine article in the 70's: 

"In real life, Glaser and Soul are friends. They don't hate each other the way many television series co-stars have done in the past. In fact, their makeup man, Shotgun Britton, once told an interviewer that, 'Those boys don't need two dressing rooms. They end up together in one dressing room. I've never seen co-stars on a show as close as these two. Even the married couples I've worked with spent more time apart!'"