Lanthanides (Ln), or rare earth elements, are detectable in trace amounts in organisms. Increased concentrations of Ln have been observed in rheumatoid arthritis (RA) in plasma (pl) and synovial fluid (Sf). We have evaluated pl and Sf concentrations of Ln (in particular La, Nd, Ce, Yb, Lu, Eu), in rheumatoid arthritis patients, before and after intra-articular steroid injection. Increased pl and Sf concentrations of Ln were confirmed in RA. No detectable synovial fluid concentrations of Ln were observed in healthy controls. A statistically significant Ln reduction (p less than 0.001) was observed in Sf 3 and 6 days after local steroid injection and in pl after 6 days. The decrease in Ln concentrations in Sf and pl, after antiphlogistic therapy, reflects the reduction of the inflammatory condition.