In 88.9% of a group of 18 patients with rheumatoid arthritis participating in an open-label study with fenoprofen calcium (Nalfon), there was observed a mean titre decrease in level of rheumatoid factor as compared to baseline levels. In follow-up, three months to one year later, a uniform titre increase above the mean level of the study period had occurred. In all cases the titre returned to baseline levels or higher.