Relatively little is known about molecular genetic events that participate in the genesis and progression of hemangiopericytoma. In this study, we describe two cases of hemangiopericytoma accompanied by severe hypoglycemia. Tumor cells from patient 1 exhibited insulin-growth factor I (IGF I) and insulin-like growth factor I receptor (IGF IR) mRNA transcripts. Tumor cells from patient 2 exhibited IGF II, IGF IR and IGF binding proteins 1-3 mRNA. Serum from patient 2 contained IGF II, mostly in a large molecular form ("big" IGF II); the IGF II level did not change after the tumor removal. The presence of IGF IR in tumor cells was confirmed by immunoprecipitation with antibodies that recognize human IGF IR subunit (visualized as a 460-kDa band). The hemangiopericytoma cells derived from patient 1 expressed 210000 IGF I receptors/cell. Specific binding of IGF I to the tumor cell membrane fraction was higher in tissue from patient 1, while the tissue of patient 2 showed relatively low IGF I binding. In contrast, IGF II binding was much higher in tissue from patient 2. Both tumor tissues showed positive immunostaining for c-Jun; one tumor showed strong immunostaining for c-Myc, H-Ras and p53, while the other exhibited strong reaction with H-Ras antibodies only. No loss of the heterozygosity at the genes APC, NFI and nm23-H1 loci in tumor tissue obtained from patient 1 was found. In effect, our results suggest multiple molecular genetic changes in hemangiopericytoma -- activation of some oncogenes and the IGF growth factor family. IGF ligands together with IGF IR could be responsible for hypoglycemia and perhaps the transformed phenotype.