The risk of mergers and acquisitions (M&A) is very high. The companies will take the consequences of those transactions for a very long time. Despite the risk, many firms decide to take part in M&A processes.The interesting aspect of M&A is the investors' reaction on planned consolidations. This reaction can be measured by CAR method (cumulative abnormal return). This method helps to estimate the real rate of return for company shares on the ground of the previous quotation. The article presents one of the most famous mergers at the Polish market in 2006 - the merger of the 'Vistula' and 'Wolczanka S.A.'