Validation of the microarray data by real-time RT-PCR was attempted in RA, OA, and NC samples for the genes IL13, MAPK8, SMAD2, IL2RG, PLCB1, and ATF5. In three cases (50%), the results of microarray analyses and real-time RT-PCR were equivalent for RA versus NC (MAPK8: variance-fold 9.8 versus 5.2; IL2RG: variance-fold 5.6 versus 8.9; ATF5: variance-fold 1.7 versus 2.3); in addition, two cases (33%) tended to result in comparable variance-fold values for microarray and real-time RT-PCR (IL13: variance-fold 12 versus 1.3; SMAD2: variance-fold 5 versus 1.1). The gene discussed is MAPK8; the disease is rheumatoid arthritis.