Acetylsalicylic acid in daily doses from 3 to 6g was prescribed to 8 patients with rheumatoid arthritis. Various assessments of clinical effect, as well as steady-state plasma concentrations and degree of plasma protein binding, were determined at each dose. The unbound fraction of salicylate increased with the dose, resulting in very high free concentrations of drug in some patients. No statistically significant relationship between total or unbound plasma concentration and the measurements of clinical efficacy were obtained. The marked increase with the dose in unbound salicylate concentration is interpreted as the result of the saturable elimination known to occur for this drug.