Pre-operative staging of rectal cancer might define patients with disease confined to the rectal wall without lymph node metastases, in whom local excision might be appropriate, or patients with extrarectal spread, who might benefit from pre-operative radiotherapy. With these objectives, 36 consecutive patients with rectal cancer were studied by endoluminal ultrasound: 17 of them also underwent computed tomography (CT) of the pelvis. The results were correlated with the findings at operation and subsequent pathological examination. Endoluminal ultrasound correctly predicted invasion of the tumour through the rectal wall in 86 per cent of patients, with a sensitivity of 96 per cent and specificity of 50 per cent, but correctly identified lymph node metastases in only 61 per cent of patients (sensitivity 57 per cent; specificity 64 per cent). CT correctly predicted invasion through the rectal wall in 94 per cent of cases, with a sensitivity of 100 per cent and specificity of 67 per cent and correctly identified lymph node metastases in 70 per cent of patients (sensitivity 25 per cent; specificity 85 per cent). These findings indicate that both endoluminal ultrasound and CT may be helpful in selecting patients for pre-operative radiotherapy. Neither technique, however, can reliably identify lymph node metastases and therefore cannot be used to select patients who would be suitable for local excision.