Growth in the importance of investments undertaken by companies and enterprises is one of the symptoms of modern economy. These investments are strongly focused on social aspects at a microeconomic level. The article presents the concept and approach to the assessment of profitability of this new category - social investments (SPI). The concept covers discussions on a definition of social investment and shows how it is possible to benefit from its implementation. The methodology of assessing profitability based on the cost benefit analysis (CBA) has been also briefly discussed. The article touches upon the CBA method, presenting:

• method assumptions,
• method algorithm,
• decision criterion based on the CBA method,
• advantages and disadvantages of the CBA method.

A need of a comprehensive identification of costs and benefits, related to the social investment, by the beneficiaries (stockholders) constitutes a new issue which is connected with the profitability assessment of these investments. So far, it has been regarded in theory and even more in practice that it is not a function which should be fulfilled by microeconomic investors.

Due to the fact that the issues related to setting the discount rate in the effectiveness account ? from the commercial, and especially, social point of view ? are still highly debatable and uncompleted; the article also focuses on the description of the way of defining a social discount rate used in the assessment of SPI profitability based on the CBA method.

When discussing the results of survey carried out among the students of the Warsaw School of Economics (SGH), the authors of the article recommend using experimental techniques of setting the social discount rate. The survey was carried out in April and May 2005.