Protooncogene expression was determined in cultured human fibroblasts derived from donors diagnosed with Hutchinson-Gilford Syndrome (Progeria). An increased level of c-myc expression was noted in progeria cells compared to normal parental controls and unrelated, unaffected, age-matched controls. In two progeria cultures a 150% increase in c-myc expression was observed, while a third progeria culture, subsequently identified as a non-classic progeria showed a 45% increase in c-myc expression. Southern blot analysis did not indicate an amplification or translocation of the c-myc gene. No significant differences were found in the expression of the c-erbB or c-src protooncogenes.