We treated one hundred patients who had various high risk solid tumors (malignant melanomas, osteosarcomas and lung cancers) by immunostimulation alone or with a sequential and synchronized chemotherapy as a complement treatment. Institut Pasteur BCG (150 mg) was administered either by scarifications (10 X 10 of 5 cm each) or multiple puncture technique (Gun), or in the case of 12 patients, by intra-tumor injections. The following complications were observed: chills and high fever during 1 to 30 days after scarifications or gun technique. In some cases an allergic loco-regional cutaneous reaction was noted after the gun technique. Nevertheless these complications were well tolerated. However, severe reactions were observed after the intra-tumor injections: malaise, chills, sweating, hyperthermia, nausea, vomiting and changes in blood pressure. In 1 case a prolonged high fever (3 weeks) was offset only by the use of corticosteroids. In another case the patient developed hepatitis. A percutaneous liver biopsy revealed noncaseating granulomas and the presence of acid fast organisms in the liver (by means of staining by auramine and observation by fluorescence). In this patient BCG has been replaced by Corynebacterium parvum (2 X 2 mg a week). This type of adjuvant was used in 2 patients and produced the same complications as the BCG. We believe that caution must be exercised in the use of such intra-tumoral treatments. BCG must be given in the hospital and patients must receive antihistaminic preparation before and after immunostimulation.