The aim of the present study was to test which tasks are suitable for work in open-plan offices according to how susceptible they are to disruption produced by the mere presence of irrelevant speech. The tasks were chosen to tap fundamental capacities of office work involving: search for relevant information, remembering material, counting, and generation of words. The hypothesis was that tasks requiring semantic processing should be impaired by irrelevant speech. To determine the magnitude of performance decrease, two sound conditions (quiet, irrelevant speech) were compared. The results showed that tasks based on episodic short-term-memory and rehearsal of the presented material were more sensitive to disruption by irrelevant speech than tasks which did not require rehearsal or were based on long-term memory retrieval. The present study points to the inappropriateness of tasks, such as information search and remembering of material, for work environments within which irrelevant speech is ubiquitous.