Thirty-one patients with a diagnosed malignant tumour of the oral cavity or pharynx were tested in hole size identification on four test occasions: before all treatment, after radiotherapy and 6 months and 1 year after surgical treatment. They were compared within groups as well as with a group of healthy reference individuals of the same age who underwent the same test procedure at a 2 months' interval. The oral group did not decline in hole size identification after radiotherapy, but did after surgery. The deterioration was persistent 1 year after surgery. The pharyngeal group did not change performance in hole size identification after radiotherapy, nor after surgery. It is obvious that surgery of the oral structures causes the deterioration. No correlation with damage to the lingual nerve could be registered. The oral cavity reacts as one unit, despite sensory input from two sides. The non-operated side does not compensate for the operated side. It is plausible that decreased oral sensory acuity, in recognizing hole size of the bolus, contributes to postoperative swallowing problems.