A group of racehorses in training was examined on several occasions with a fibreoptic endoscope and monitored for viral infection. Only equine herpes virus-2 (EHV-2) infection was detected. Pharyngeal lymphoid hyperplasia (PLH) was present in all horses and decreased in severity with age. There was no association between PLH severity and antibody titres to EHV-1, or with the isolation of EHV-2. Finishing position in races was not affected by PLH severity. Exercise induced pulmonary haemorrhage (EIPH) was evident on 23 out of 49 (47 per cent) examinations after maximal speed training exercise. Eighteen out of 19 (95 per cent) horses examined on at least two occasions had EIPH but its occurrence was not predictable. Observable mucoid or mucopurulent exudate was present in the trachea in 60 out of 118 (50 per cent) examinations and the amount seen was increased following exercise.