Provided is a novel pharmaceutical use of a pyrazolidinedione derivative represented by the following formula, which has an action of suppressing activation of Rac via DOCK2, DOCK180 or DOCK5. Specifically, it provides a pharmaceutical use as a preventive or therapeutic agent for various immune-related diseases such as Rac activity-related diseases such as autoimmune diseases and malignant tumors, and an immunosuppressive agent. [In the formula, Z represents methine (CH) or a nitrogen atom (N), X represents a substituent represented by the following formula: R 1 and R 2 are the same or different and represent a hydrogen atom, a halogen atom, a hydroxyl group, Or an alkyl group having 1 to 4 carbon atoms. n means an integer of 0-2. ].DOCK2、DOCK180またはDOCK5を介したRacの活性化を抑制する作用を有する、下式で示されるピラゾリジンジオン誘導体の新規医薬用途を提供する。具体的にはRac活性関連疾患、例えば自己免疫疾患などの各種免疫関連疾患や悪性腫瘍の予防または治療剤、並びに免疫抑制剤としての医薬用途を提供する。〔式中、Ｚはメチン（C-H）または窒素原子（N）を示し、Ｘは下式で示される置換基を意味し：Ｒ1及びＲ2は、同一又は異なって、水素原子、ハロゲン原子、水酸基、または炭素数１～４のアルキル基を示す。ｎは０～２の整数を意味する。〕。
