OBJECTIVE: To study patients with side effects secondary to the injection of modelants. METHODS: We studied their clinical, serological, histopathological, radiographic, immunoregulatory and fibroblast culture features by standard methods. We studied thirty patients, 24 women, mean age: 38.2 years. Patients had received either mineral oil, guayacol, silicone or a mixture of these substances; some had received unknown material(s). RESULTS: The mean time between the injection and the onset of symptoms was six years (range: 0.1-24 years). All patients had sclerodermatous skin changes, subcutaneous nodules, edema and/or hyperpigmentation at the site(s) of injection(s); five individuals also had skin changes at sites remote from the injection. Thirteen patients had clinical features of an autoimmune disease. Eleven patients gave a history of arthralgias including four that had symmetrical non-erosive polyarthritis. Twenty of 28 patients (71%) had positive anti-nuclear antibodies. We found intracellular spontaneous production of IL-1 (interleukin-1) by patients' macrophages which was almost absent in normal cells (p < 0.001). Silica-stimulated monocytes from patients also secreted more IL-1 than those from normal subjects (p < 0.001) in autologous mixed lymphocyte reaction. Twelve patients had an early proliferative response. At day seven, a decreased proliferative response was seen in 12/19 patients (p < 0.001). Skin fibroblasts from 3/3 patients synthesized 3-to-5-fold more 3H-hyaluronic acid than normal control cells (p < 0.001). CONCLUSIONS: This report confirms the association between the injection of modelants and the development of autoimmune disease (human adjuvant disease, HAD). Our results implicate IL-1 in the amplification of the disease process. The similarities between primary scleroderma and human adjuvant disease now include immunological and connective tissue data. The study of these patients may help to understand the etiopathogenesis of some autoimmune diseases.