Stock exchange indices are an important information basis for investment decisions, but also for decisions on macroeconomic policies. Although these indices largely reflect speculative activities, certain statistical procedures can nonetheless identify' the factors which influence their changes. This topic has not received due attention ever since the Republic of Croatia adopted the system of free market economy. In order to decrease such information insufficiency and to improve the decision-making process, this paper will present a model of establishing determinants of the Zagreb Stock Exchange index CROBEX. The construction and implementation of the model is based on computer support.