A double blind, randomized, parallel group clinical therapeutic trial, comparing a sustained release formulation with a standard preparation of tiaprofenic acid (Surgam), was performed in 119 patients with rheumatoid arthritis. The sustained release preparation was prescribed as two 300 mg capsules taken once a day, and the standard formulation as one tablet of 300 mg taken twice a day. From baseline up to the 3rd and 6th week of treatment, a statistically significant difference (p less than 0.001) was observed in both treatment groups for all the variables, indicating objective or subjective changes in the clinical signs and symptoms of the patients. For most of these variables, no significant differences were observed between the sustained release and the standard formulations. Also, no significant differences were observed between the 2 formulations in the incidence of side effects and abnormal laboratory findings.