Oliguria in patients following spinal cord injury was first mentioned in 1649, but has since been referred to only occasionally. The work detailed here was completed 30 years ago but is reported because of the lack of any comparable study and because suitable patients are not now readily available. A total of 27 water load tests were carried out on 20 patients. The test included measurement of serum osmolality to confirm absorption of ingested water. Impaired response to the water load was obtained in 17 tests: 12/13 between 1 and 5 days after onset of the cord lesion and 5/14 more than 2 weeks after injury. The possibilities that oliguria was due to dehydration, failure to absorb ingested water, hypotension or renal failure are discounted. In the first few days after injury, oliguria may be due to release of antidiuretic hormone as part of the metabolic response to trauma. The impaired response seen later is discussed in relation to possible neural and hormonal mechanisms. There is a need for further study of factors influencing water excretion in tetraplegic and paraplegic patients.