As laboratory investigation is essential for the diagnosis of Legionnaires' Disease, the lack of immediate access to a suitable laboratory may result in under, or late, diagnosis. Recently, there has been emphasis on culture as the principal means of diagnosis. This survey describes the diagnostic facilities for Legionnaires' Disease in Scottish hospitals, particularly in relation to the role of the acting reference laboratory in Ruchill Hospital, Glasgow. Facilities have clearly been expanding, with six laboratories setting up local services since 1985. In 1990, 16 out of 36 laboratories (44%) in 10 out of 15 health boards offered diagnostic tests for Legionnaires' Disease; of these 14 offered culture. All laboratories used the acting reference laboratory (directly or indirectly) to confirm positive results. Three laboratories stated that they would test all specimens from patients with pneumonia; the others would do so only on request or when indicated by clinical judgement. These findings provide confidence about the completeness of the surveillance data compiled at the acting reference laboratory and make easier the interpretation of information about geographical and secular variations in disease incidence. Further expansion of diagnostic facilities, particularly culture, with continuing use of the acting reference laboratory for more complex tests, conformation of results and quality control, would meet the objectives of early diagnosis and effective surveillance.