BACKGROUND Infliximab is a chimeric monoclonal antibody directed against tumour necrosis factor-alpha that has been shown to improve chronic refractory and fistulating Crohn's disease. Infliximab infusions have been associated both with immediate and delayed reactions. METHODS Desensitisation was performed in four patients who had experienced immediate reactions to infliximab infusions and in one who had developed a delayed reaction. No therapeutic alternatives were available for these patients. Before desensitisation, skin tests were performed. RESULTS Skin-tests were negative for all patients. Desensitisation was performed with serial dilutions of infliximab with monitoring of vital signs before each increment. After parenteral desensitisation, all five patients were able to tolerate infliximab infusion without complications or any requirement for antihistamines or steroids. However, two patients who had initially presented with an immediate reaction to infliximab experienced arthralgia and myalgia similar to a "serum sickness-type" of reaction 6 to 10 days after desensitisation. CONCLUSIONS Even if there is no evidence of an allergic mechanism in infusion reactions to infliximab, successful desensitization can be achieved for patients experiencing acute reactions. The mechanism of desensitisation remains presently unknown. It is not yet possible to say if desensitization will be effective in preventing delayed reactions.