The objective of this study was to evaluate if there are early clinical parameters in AS patients treated with three standard infusions of infliximab, which would predict whether a patient will derive a significant improvement at the tenth week, or whether there will be a lengthy clinical response after discontinuing the infusions. Sixty three AS patients were given three infusions of 5 mg/kg of infliximab at weeks 0, 2, and 6 and evaluated serially before each infusion and also at week 10. Afterwards, patients were followed up by telephone interview until their disease activities were >60% of the baseline values. At that point, disease was considered to have relapsed. Clinical parameters at baseline as well as at week 2 were used for analysis to identify factors that might predict an improvement at week 10, or predict a delayed relapse. A predictor is regarded as being useful if the area under the curve (AUC) when analyzed by receiver operator calculations (ROC) exceeds 0.75. No parameters at baseline have sufficient predictive values. However, ASAS20 (Assessment in Ankylosing Spondylitis International Working Group criteria) at week 2 predicts improvement at week 10, and also duration of clinical response after discontinuing the infliximab at week 6. The response to one pulse of infliximab is the best predictor of subsequent response as well as rate of relapse after discontinuing the infliximab.