The effects of quartz (14808607) and coal dusts on fibroblast proliferation from human macrophages were studied in-vitro. Human macrophages derived from monocytes were cultured and incubated with suspensions containing 30 micrograms per milliliter DQ-12, a reference quartz, or coal mine dust obtained from the Ruhr, Federal Republic of Germany (TF-1 dust), at dilutions up to 1:40 for 24 hours. The cultures were then filtered and the supernatant was collected. The supernatants were added to cultures of the human fibroblast lines FH-3, MRHF, or WI-38. The effects on fibroblast growth were assessed by measuring changes in protein concentration. The supernatants from quartz or coal dust treated macrophages caused significant increases in the growth of FH-3 fibroblasts at all dilutions. A similar effect was seen when WI-38 fibroblasts were treated with supernatants from coal dust treated macrophages. Since the data suggested that the supernatants from quartz or coal dust treated macrophages contained one or more soluble factors that stimulated fibroblast growth, efforts were made to characterize the factor. The supernatants from quartz and coal dust treated macrophages were heated at 56 degrees-C for 60 minutes before being tested with FH-3 fibroblasts. The supernatants were centrifuged and filtered through millipore filters having molecular weight limits of 10 and 30 kilodaltons (kDa) and then tested for their ability to stimulate growth in MRHF and FH-3 fibroblasts. The data were used to estimate the molecular weight of the factor. Supernatants from quartz or coal dust treated macrophages were still active after being heated at 56 degrees for 1 hour. The molecular weight of the factor was estimated to be greater than 30kDa. The authors conclude that human macrophages derived from blood monocytes when cultured form a soluble factor after being incubated with quartz-D12 or TF-1 dust that has a stimulatory effect on human fibroblast growth. This factor is designated fibroblast proliferation factor.