The medical emergency team (MET) at Liverpool Hospital superseded the cardiac arrest team in 1990 and can be summoned by any staff member who identifies a patient at risk according to preset criteria; for example, severe hypotension. Weekly reviews of MET calls have identified clinical antecedents present prior to the patient's condition deteriorating to a critical level. This study assessed the responses of nurses in the presence of these warning signs. Medical records of 178 patients who required MET assistance during 1994 were retrospectively reviewed. A data collection form designed for the study sought demographic information, time and location off the MET call and documented patient complaints for the 24 hours preceding the MET call. Also collected was information on who was contacted as a result of the critical observation. Analysis included frequencies, percentages, means and standard deviations, including location, type and timing of the MET call. MET calls occurred in the general wards (50 per cent), emergency department (42.3 per cent) and other areas (7.7 per cent). The four main categories of emergency comprised cardiac arrest (25.6 per cent), airway/breathing problems (22 per cent), decreased level of consciousness (20.8 per cent) and 'other', including prolonged chest pain, fitting and hypotension (31.6 per cent). The predominant response to a clinical antecedent was to call the MET (68.4 per cent). Other responses resulted in delays of 1 hour (18 per cent) and up to 3 hours (8 per cent) on some wards before treatment specific to the clinical antecedent commenced. A need to educate health professionals regarding the warning signs of acute severe illness and when to summon assistance has been identified.