1. Scleroderma is a systemic autoimmune disorder characterized by fibrosis affecting the skin, lung, kidney and other organs. The 70 kDa heat-shock protein has been implicated as essential for cell function during cell growth and differentiation. To study the molecular basis of intracellular events in sclerotic fibroblasts, we compared the expression of the hsp 70 gene in sclerotic and normal control fibroblasts by a run on nuclear transcription assay and a Northern blot assay. 2. In the run on nuclear transcription assay, sclerotic fibroblasts expressed an approximately eightfold higher level of hsp 70 transcription than normal fibroblasts in the quiescent condition after serum starvation. After stimulation with serum, the transcription level of the hsp 70 gene was almost similar in sclerotic and normal control fibroblasts. 3. In the Northern blot assay, the hsp 70 gene transcript, which was present in increased amounts in sclerotic fibroblasts, exhibited normal size.