Prospective study carried out on 24 consecutive patients with Crohn's Disease, using sonography to assess changes caused by biological therapy and its relationship with the clinical-biological response. The Crohn's Disease Activity Index, the plasma concentration of C-reactive protein and abdominal sonograms (to assess the thickness and Doppler flow grade of the bowel wall and to detect the presence of any complications) were carried out one week prior to the induction treatment and two weeks after. The biological therapy induced remission or a partial response in 46% and 25% of the patients, respectively. It also caused a significant reduction in the thickness of the bowel wall (P = 0.005) and Doppler flow (P = 0.02), leading to the disappearance of complications in 50% of the patients. Sonographic changes were significantly more marked in patients who achieved some type of clinical-biological response, in such a way that sonograms were improved in 65% (P = 0.001) and complications disappeared in 100% of patients (P = 0.005) compared to those patients who did not respond to treatment. However, sonographic normality was only achieved in five out of 17 (29%) reactive patients (P = 0.27). This fact may support the use of sonography as a technique for optimizing the biological treatment of Crohn's Disease.