The process of intimal thickening after arterial injury can be divided into several steps, namely, initiation of smooth muscle cell proliferation, migration, and further intimal proliferation and deposition of matrix. Factors controlling the initiation of proliferation include de-endothelialization and vessel distension but not platelet adherence. Migration and subsequent intimal proliferation are controlled by factors from platelets, re-endothelialization, and endogenously released gamma-interferon.