Interleukin 2 (IL 2) production was studied in lymphoid cells from rats undergoing an acute non specific inflammatory reaction induced by intrapleural injection of calcium pyrophosphate. Spleen and lymph node cells derived from inflamed animals had an increased level of IL 2 like production compared to cells from normal animals. Thymocytes also showed enhanced IL 2 like production although the absolute levels were lower than spleen or lymph node cells. It has been suggested that the acute non specific inflammatory reaction is able to modify lymphocyte reactivity via IL 2 and interleukin 1 (IL 1). The nature of the humoral factors released by the inflammatory process which are capable of initiating these events is also discussed.