The systemic inflammatory response syndrome (SIRS) is defined by abnormal temperature, heart rate, minute ventilation or white cell count and can be due to infectious or non-infectious causes. In a single day, 23% of hospital ward patients fulfilled SIRS criteria. Patients with SIRS were more likely to be under medical than surgical units. One-third of the patients had evidence of infection. There was no association between SIRS criteria and increased mortality or hospital length of stay.