We have used transgenic male mice not expressing interleukin-6 (IL-6) [C57BL/6J(IL-6/-tm Kopf)] in object recognition test to assess the role of endogenous IL-6 in recognition memory. Wild-type controls showed better memory than IL-6 knock-out mice. Results of our experiment suggest that endogenous IL-6 may play an important role in the process of recognition memory in mice.