1. Increased spontaneous production of interleukin-1, measured as lymphocyte-activating factor activity, was seen in unstimulated monocytes from systemic sclerosis patients.
2. Inhibitory activity to interleukin-1 was seen in both normal and patient monocyte supernatants.
3. Inhibitory activity was significantly higher in unstimulated and stimulated monocyte supernatants from systemic sclerosis patients.
4. The net effect was an apparent decrease in lymphocyte-activating factor activity in the monocyte supernatants from systemic sclerosis patients.
5. These findings suggest a possible mechanism by which collagen deposition could be enhanced, thereby giving rise to the extensive fibrosis characteristic of systemic sclerosis.