Irritable bowel syndrome (IBS) has been associated with visceral hypersensitivity. Here we examined the evolution of rectal sensitivity and of gastrointestinal symptomatology in IBS patients over time, to verify if the clinical and biological parameters showed parallel behavior. Patients complaining of IBS, identified by Rome 1 criteria, were included in this study. The severity of the gastrointestinal (Gastrointestinal) symptoms was assessed by a gastrointestinal index. The pain threshold to rectal distension was measured by a barostat programmed for phasic ascending distensions. Both measures were obtained before and after treatment. Thirty-nine patients were followed while on a 10-week group psychotherapy (psy) program. Twelve patients were controlled after pharmacological treatment with amitriptyline (Ami) 10 mg hours for two weeks and then 25 mg hours for the following 4 weeks. Clinical improvement with symptom reduction was achieved in both patients groups. With psy, the Gastrointestinal index declined from an initial value of 78.4 +/- 4.8 to 65.5 +/- 4.5 at the end of treatment (P < 0.05). With Ami, the gastrointestinal index decreased from 91.6 +/- 5.6 to 61.8 +/- 9.1 (p < 0.01). The pain threshold to rectal distension increased from 27.7 +/- 1.0 to 33.7 +/- 1.9 mmHg (P < 0.01) after drug treatment, but remained unchanged (30.6 +/- 1.0 vs 30.6 +/- 1.1 mm Hg) with psy. Evolution of the gastrointestinal index and rectal sensitivity were directly correlated (r = -0.71; P < 0.01) in Ami patients, but not in those treated with Psy (r = -0.001). In conclusion, visceral hypersensitivity appeared as a stable biological defect over a 10- to 12-week period during clinically-effective treatment with psychotherapy. Rectal pain threshold, however, seemed to be pharmacologically manipulatable in patients treated with Ami.