C-reactive protein (CRP) was measured serially in 16 patients with an acute spinal injury. Twelve episodes of acute urinary tract infection (UTI) occurred during the study period. These were all associated with an increased concentration of CRP greater than 50 mg/l, which returned to normal after successful treatment. Thirteen episodes of asymptomatic bacteriuria associated with increased concentrations of CRP greater than 20 mg/l occurred, indicating tissue damage. More commonly, significant bacteriuria was associated with normal concentrations of CRP, and presumably, simple colonisation of the urinary tract, which, we suggest, does not require treatment with antibiotics. Serial measurement of CRP in patients with spinal injury may help distinguish between urinary tract colonisation and infection and be useful in monitoring the response to the treatment of clinical UTI.