The international research on corporate governance focuses i.a. on the influence of legal rules on the economic performance and organisation of the firm. This paper analyses the evolution of the ownership structure of Belgian stock exchange listed companies. The concentration of blockholders rises significantly during the period 1985-1989, the year of the introduction of the mandatory take over bid. By enlarging their stake, large shareholders didn't have to start a take over bid. They receive the controlpremium when selling the stake.