In this study the possible cytostatic effects of eupatoriopicrin, a sesquiterpene lactone isolated from Eupatoriurn cannabinurn L., against the fibrosarcoma FIO 26 have been investigated. This solidly growing tumour was transplanted subcutaneously in C57BI mice. Eupatoriopicrin was administered intraperitoneally (as single as well as repeated doses) as a solution in 20% v/v ethanol. Different doses and dosage schedules were used and compared with control conditions. A dose dependent growth delay of the tumour was found. The treating volume of the tumour was about 500 pl. Two clinically applied chemotherapeutics, doxorubicin and cyclophosphamide, were used as reference compounds.