Infliximab, a monoclonal chimeric anti-tumor necrosis factor alpha (anti-TNF-alpha) antibody, was tried in two patients suffering from severe refractory juvenile ankylosing spondylarthritis with disease duration of more than 10 years. To assess the response, validated clinical activity parameters were monitored prospectively. In both patients, treatment with infliximab at a dosage of 5 mg/kg body weight already led to considerable improvement with loss of joint pain the day after it was given. Bath Ankylosing Spondylitis Functional Index scores decreased from 5.8 to 0 and 7.2 to 1.0 and the Bath Ankylosing Spondylitis Disease Activity Index from 2.6 to 1.4 and 9.0 to 1.0. In one patient, the response to a single infusion continued for more than 8 months. Because of a recurrence of symptoms in intervals of 2 months, the fourth infusion has now been given to the second patient, resulting in immediate clinical response. No side effects have been noted. Infliximab seems to be a promising agent for treatment of active and refractory juvenile ankylosing spondylitis. Controlled studies and long-term observations are warranted.