Systemic idiopathic fibrosis with T-cell receptor gene rearrangement. A case of systemic idiopathic fibrosis was analyzed by Southern blotting with probes to the immunoglobulin heavy chain and T-cell receptor genes. A 45-year-old man presented with bilateral neck swelling. He later developed lower back pain, and findings on a computed tomographic scan were consistent with idiopathic retroperitoneal fibrosis. A biopsy specimen of a neck lesion showed morphologic characteristics typical of idiopathic fibrosing cervicitis. Immunophenotyping of the lesion revealed a polymorphic lymphoid population. Molecular analysis with the use of probes to the immunoglobulin and T-cell receptor genes disclosed a germline DNA pattern for the immunoglobulin gene and a rearranged pattern for the T-cell receptor gene. 