The introduction of biological treatments like monoclonal anti TNF-a antibodies (infliximab), is changing the clinical history of Crohn's disease (CD). The effects of these therapies are monitored emplying clinical indexes of active disease, laboratory parameters, endoscopy and histology, and also with imaging techniques. A new ultrasound contrast agent, SonoVue (Bracco SpA, Milano, Italy), is opening new perspectives in the study of microvasculature of several organs. Aim of this study is to evaluate by SonoVue enhanced ultrasonography (US) the occurrence of modifications in bowel wall microvasculature of CD patients and to correlate them with parameters of disease activity and to follow up the findings during infliximab therapy. After performing a basal color-doppler ultrasonography, the study of the affected bowel loop is performed after i.v. injection of SonoVue and the enhancement is evaluated on a qualitative basis. We report on the preliminary results obtained in twenty patients, eight of which have been treated with three infusions of infliximab (induction cycle) and evaluated at baseline and after the treatment. While at baseline we describe a positive correlation of SonoVue enhancement of the affected bowel loop with CRP, alpha1-glycoprotein and white blood cell number, after infliximab treatment in 6/8 cases a definite improvement was detected. Ultrasonographic evaluation of the changes of bowel wall enhancement after i.v. SonoVue during infliximab therapy might represent an useful, not invasive and relatively low cost imaging modality for the clinical monitoring of activity of small bowel Crohn's disease.