BACKGROUND The Laryngeal Tube Sonda (LTS) is a supraglottic airway which, like the ProSeal Laryngeal Mask Airway (PLMA), incorporates a drain tube. We compared the performances of LTS and PLMA during controlled ventilation anaesthesia. METHODS The devices were studied in 32 ventilated patients by randomized crossover trial. Primary outcome was airway seal pressure. Secondary outcomes included insertion success and time, manipulations required, ventilation quality, peak and plateau airway pressures, ability to pass a gastric tube and fibreoptic laryngeal view. RESULTS The PLMA produced a higher seal pressure (median values, PLMA 26 cm H(2)O and LTS 24 cm H(2)O, P<0.01). First-attempt insertion succeeded with PLMA 28 times and LTS 22 times (P>0.05). The PLMA required fewer manipulations (P<0.05) in fewer patients (P<0.05) and took less time to insert (P<0.01). All PLMA patients and 22 LTS patients achieved optimal ventilation (P<0.01). Peak airway pressure was lower with the PLMA than with the LTS (P<0.01). The vocal cords were visible through the PLMA in 32 patients and through the LTS in nine patients (P<0.001). The laryngeal view was superior through the PLMA (P<0.001). CONCLUSIONS The difference in seal pressure between devices was clinically unimportant. However, the LTS had an unexpectedly high failure rate. PLMA performance exceeded LTS performance in many clinically useful measures. The PLMA has greater clinical utility than the LTS during controlled ventilation.