Changes in monitoring and therapy during the preparation of 100 critically ill patients for interhospital transfer by a specialist team were documented prospectively with the aim of providing guidelines for nonspecialists. Severity of illness scores were recorded before and after preparation. Median duration of preparation for ambulance journeys was 50 min and for aeroplane journeys was 82 min. During preparation, a portable electrocardiogram and pulse oximeter were attached to 21 and 76 patients respectively and intra-arterial pressure monitoring was continued or instituted in 88 patients. Supplemental oxygen and intravenous fluids were the therapies most commonly increased or instituted by the transport team; mechanical ventilation, positive end-expiratory pressure and inotropic drugs were increased or instituted less frequently. Median therapeutic intervention scores before and after preparation were 21 and 23 respectively, highlighting the need to increase rather than withdraw support for transfer.