The first two thirds of the 62-minute broadcast were presented as a series of simulated news bulletins, which suggested to many listeners that an actual alien invasion by Martians was currently in progress. Compounding the issue was the fact that the Mercury Theatre on the Air was a sustaining show (it ran without commercial breaks), adding to the program's realism. Although there were sensationalist accounts in the press about a supposed panic in response to the broadcast, the precise extent of listener response has been debated, particularly since the show was not drawing a large share of the radio audience. Many more Americans were listening to Edgar Bergen; however, when Bergen's opening comedy routine ended and gave way to a musical interlude, many people may have started turning the radio dial to see what else was on. Those people found a radio show that sounded like a real account of an alien attack. The show did issue a disclaimer at the beginning of the show, but the people tuning in late did not hear that announcement and so a small panic did occur.

Later studies indicate that many missed the repeated notices about the broadcast being fictional, partly because The Mercury Theatre on the Air, an unsponsored cultural program with a relatively small audience, ran at the same time as the NBC Red Network's popular Chase and Sanborn Hour, by ventriloquist Edgar Bergen. About 15 minutes into Chase and Sanborn, the first comic sketch ended and a musical number began, and many listeners supposedly began tuning around the dial at that point.

According to the American Experience program The Battle Over Citizen Kane, Welles knew the schedule of Chase and Sanborn and scheduled the first report from Grover's Mill at the 12-minute mark to heighten the audience's confusion. As a result, some listeners happened upon the CBS broadcast at the point the Martians emerge from their spacecraft. Because the broadcast was unsponsored, Welles and company could schedule breaks at will rather than structuring them around necessary advertisements. As a result, the only notices that the broadcast was fictional came at the start of the broadcast and about 40 and 55 minutes into it.