Bcl-2 is one of the many proteins that regulate programmed cell death and is overexpressed in B-cell lymphomas. The expression of bcl-2 in mesenchymal cells and soft tissue tumours was the subject of this study. Normal mesenchymal tissue and representative cases of soft tissue tumours of different types (n>200) were investigated immunohistochemically for bcl-2 expression. Although bcl-2 expression was normally relatively restricted to some smooth muscle cells and neural cells, bcl-2 immunoreactivity was widespread in different types of soft tissue neoplasms, both benign and malignant. Consistently positive tumours included solitary fibrous tumour, haemangiopericytoma, schwannoma and synovial sarcoma. The few soft tissue tumours that were consistently negative for bcl-2 included nodular fasciitis and desmoid tumour. Leiomyomas and leiomyosarcomas were heterogeneous; all uterine leiomyomas were bcl-2 positive, but all oesophageal leiomyomas were negative, paralleling the reactivity observed in the smooth muscle at those sites. Gastrointestinal stromal tumours showed bcl-2 reactivity; this was less consistent in malignant tumours. Along the malignancy gradient, there was no consistent trend in the bcl-2 reactivity. Dermatofibrosarcomas showed increase of bcl-2 expression with fibrosarcomatous transformation, whereas smooth muscle sarcomas and malignant peripheral nerve sheath sarcomas were less consistently positive than the corresponding benign neoplasms. We conclude that bcl-2 expression is widespread in soft tissue tumours, but shows constitutional expression patterns that are often parallel to the normal tissue counterparts. Compared with benign soft tissue tumours, bcl-2 expression is often reduced in sarcomas, but it cannot be used as a prognostic marker without correlation of the data to its phenotypic expression patterns.