This is a single site, placebo- controlled, double-blind study to test the efficacy of ENBREL (TNFR:Fc fusion protein) produced by Immunex in patients with ankylosing spondylitis. The protocol involves 40 patients randomized to either placebo or subcutaneous ENBREL twice weekly for 4 months. Outcomes will be measured with standard AS instruments. This is an important study that will provide the rational evidence to support administering ENBREL to AS patients.