Three experiments examine what is widely reported to be one of the most common forms of interference in open-plan office environments—the effect of background noise. Experiment 1 investigates whether office noise (with or without speech) is disruptive to two office-related tasks: memory for prose and mental arithmetic. The results show that whereas office noise with speech disrupts performance on both tasks, office noise without speech disrupts performance on the mental arithmetic task only. Experiment 2 investigates the memory for prose task more closely by varying the duration and the meaning of the background noise. Experiment 3 examines whether the meaning of speech is important to the disruption of a mental arithmetic task. The results show that both speech and office noise can disrupt performance on memory for prose and mental arithmetic tasks, and the effect is independent of the meaning of the irrelevant speech. These results are presented and interpreted in light of current research and theories regarding the effect of background noise.