ずぼらな英語学習

The cast of characters in the novel was modified for the film, most notably by changing the male Dr. Peter Leavitt in the novel into a woman, Dr. Ruth Leavitt. Screenwriter Nelson Gidding suggested the change to Wise, who at first was not enthusiastic, as he initially pictured the sex-changed Dr. Leavitt as a largely decorative character reminiscent of Raquel Welch's character in the 1966 film Fantastic Voyage. When Gidding explained his take on Leavitt, Wise resolved the question in an appropriately scientific way by asking the opinion of a number of scientists, who were unanimously enthusiastic about the idea. Eventually Wise came to be very happy with the decision to make Leavitt female, as Kate Reid's Dr. Leavitt turned out to be, in his words, "the most interesting character" in the film．　 Another minor change was the character of Burton in the novel, who became Charles Dutton in the film; no reason was given for this name change.

A young Michael Crichton makes a cameo appearance in a non-speaking role during the scene where Dr. Hall is told to break scrub because he has to report to Wildfire, the government's secret underground research facility.