Two fibreoptic bronchoscopes with insertion cords of different diameters (3.7 and 5.0 mm) were compared during fibreoptic intubation in 84 adult patients (ASA 1-2) undergoing orotracheal intubation under general anaesthesia. The fibrescope used was randomly selected. The incidence of resistance to passage of the tracheal tube through the vocal cords was higher using the thinner fibrescope, 14/40 (35%) as compared with the thicker fibrescope, 5/44 (11%) (p < 0.05). Intubation failed with the thinner fibrescope in 8/40 (20%) of patients, whereas all intubations with the thicker fibrescope were successful in six patients after manipulation of the tracheal tube (p < 0.01). With the thinner fibrescope manipulation of the tracheal tube after impingement led to intubation of the trachea in 6/14 (43%) patients. The duration of intubation was significantly shorter with the thicker fibrescope (p < 0.05). There were two instances of oesophageal intubation with the thinner fibrescope. A fibrescope with a thicker insertion cord is more suitable for orotracheal fibreoptic intubation in adult patients.