OBJECTIVE To study the relationship between reactive astrogliosis and its autocrine bFGF. METHODS On the primary astrocyte culture with mechanical scratch, the dynamic expression of bFGF, PCNA, GFAP and GFAP-mRNA were determined by immunocytochemistry and in situ hybridization. RESULTS Astrocytes at the edge of the injury began to express bFGF 2 hours after scratching and reached its peak by the 12th hour, then declined after 2 days. GFAP-mRNA was detectable in astrocytes near the injury from the 6th hour and reached its peak within 24 hours. A few hypertrophic astrocytes in the injured area expressed GFAP-mRNA on the 3rd day. Enhanced GFAP expression of astrocytes was observed with hypertrophy of cytoplasma which extended wide processes into the injured area from the day of the scratch and reached its peak on the 2nd day. On the 3rd day, the previously injured area was covered with hypertrophic astrocytes. PCNA was expressed 2 hours after damage by some of the astrocytes in the vicinity of injury. CONCLUSIONS Autocrine bFGF was the early response of reactive astrocytes and bFGF may act as promoter of reactive astrogliosis. Enhanced GFAP expression was the result of upregulation of GFAP-mRNA. The prominent event of reactive astrogliosis was the hypertrophy of astrocytes.