Fifteen subjects with rheumatoid arthritis defined as "classical" or "definite" according to A.R.A. criteria and classified according to Steinbrocker as stages I to III were submitted to knee joint infiltration (bilateral where both knees were involved) with 50 mg thymopentin in 1 ml, once a week for five weeks. Telethermographic examination was performed in all cases in order to evaluate the thermal inflammatory component before the first and 48 hours after the last infiltration. In none of the patients with the exception of only one case, did the drug lead to a significant change of the thermal index. This evaluation does not take into account any other objective and subjective parameters the study of which was beyond the scope of the above research.