The expression of insulin-like growth factor-1 (IGF-1) was studied in normal tissues, in eight benign lesions and in 50 sarcomas. In palmar fibromatosis the spindle cells in cell-dense areas exhibited a strong immunoreactivity. IGF-1 was variably found in leiomyosarcomas (7/8), malignant schwannomas (7/9), synovial sarcomas (2/3), liposarcomas (3/6), fibrosarcomas (1/3), malignant fibrous histiocytomas (10/18) and in one angiosarcoma. Two rhabdomyosarcomas failed to express IGF-1 and only the spindle cell component of synovial sarcomas was positive. Immunoreactivity for IGF-1 in 10 malignant filrous histiocytomas (MFH) appeared to be related to co-expression of smooth muscle actin. These findings imply that MFHs can be subdivided into a group of tumours which are devoid of morphological and immunophenotypic evidence of differentiation and a group which manifest immunophenotypic differentiation.