Aims: To assess whether information in general practitioner (GP) referral letters provides a basis for selection of diagnostic tests in patients referred for specialist respiratory advice. Methods:We undertook a prospective study within a respiratory outpatients department to compare the diagnostic tests planned at three stages of the referral/specialist consultation process: i) using the GP referral letter alone; ii) using the referral letter and patient history; iii) using the referral letter, patient history, and clinical examination.Results: Analysis of the content of GP referral letters revealed wide variations in referral information. A high proportion of tests selected using the referral letter alone were altered after specialist history-taking and examination. Far fewer changes were recorded between history-taking and examination.Conclusions: Neither literature review nor our study support a system which bases diagnostic test selection on GP referral letters alone. However, our findings suggest that approaches which include specialist history-taking in advance of face-to-face consultation merit further investigation.