Summary Spleen cells recovered from mice during a primary infection with Ross River virus showed a virus‐specific proliferative response when challenged in vitro. The majority of the proliferating cells were T‐lymphocytes. In contrast, there was liltle detectable migration inhibition factor produclion by these spleen cells and little or no virus‐specific cytotoxic activity. Sub‐cutaneous challenge with virus elicited a weak delayed type hypersensitivity reaction.