David Hemmings claims in his autobiography that Richard Harris was kicked off the film after he punched Antonioni, and that the scenes that were still to be completed were done with another actor who was photographed from behind. Hemmings was apparently told this when Harris warned him about Antonioni when Hemmings was working on Blow-Up (1966).
The idyllic Mediterranean story that Giuliana tells her son is the only sequence in the film in which the color was not manipulated.
The audio commentary, for the BFI DVD, states that Richard Harris walked off the film after an argument with Michelangelo Antonioni, who had told him to walk diagonally across a yard. Harris asked why, to which Antonioni answered, "You don't ask me why, you're an actor. You just do it." The film was behind schedule at this stage, and Harris was due to start work soon on Major Dundee (1965). This and his argument with Antonioni were probably what led him to walk off the film.
While making this film on location in Italy, Richard Harris experimented with LSD for the first time. He was caught climbing the Trevi fountain in Rome, and then ended up locked in a hotel bathroom, smashing the mirrors to smithereens with his bare fists.
In an interview with Jean-Luc Godard, Michelangelo Antonioni dismissed the general critical consensus that industrialization was partly responsible for the fragmenting of Giuliana's mind. He said his intention was actually to celebrate the beauty of the industrial landscape, something that Giuliana can't appreciate because of her fragile mental state.