a-defensins are released from granules of leukocytes and are implicated in inflammatory and fibrotic lung diseases. In the present study, the effects of a-defensins on the proliferation and collagen synthesis of lung fibroblasts were examined. We found thata-defensin-1 and a-defensin-2 induced dose-dependent increases in the incorporation of 5-bromo-2¢-deoxy-uridine into newly synthesized DNA in two lines of human lung fibroblasts (HFL-1 and LL-86)