A study of serum growth factors and oncoproteins in firefighters was conducted to determine if serum growth factors or oncoproteins could serve as biomarkers for the development of cancer or nonmalignant respiratory disease. The cohort of 33 New York City firefighters, mean age 55 years, was selected from among participants in a medical surveillance program. The comparisons consisted of 16 healthy medical center volunteers, mean age 54 years. Blood samples were collected and assayed for beta transforming growth factor (bTGF), platelet derived growth factor (PDGF), and the oncogene proteins ras, fes, myc, myb, mos, src, and int using an immunoblotting technique. Medical and occupational histories of the subjects were reviewed. No positive bands for PDGF, ras, fes, myc, myb, mos, src, or int were found in any of the serum samples. Fourteen firefighters were positive for bTGF, but none of the comparisons were. The bTGF positive and negative firefighters were similar with regard to age and years of employment in firefighting. Compared to the seronegative firefighters, bTGF positive firefighters were slightly more likely to have abnormal chest X-rays, a prior history of asbestos (1332214) exposure, fewer pulmonary complaints, and to be nonsmokers. None of the differences were statistically significant. The authors conclude that bGTF may be related to pathological processes induced by firefighting exposure. It may be suitable for monitoring pathological changes related to nonmalignant respiratory disease or cancer in firefighters and other exposed populations.