The goal of this paper is to desigen a system for the detection and evaluation of the decrease of drivers’ attention. The paper refers to possible reasons and risks of a phenomenon called micro-sleep. It also describes the measurement methodology. The paper apprise of a new way of detection and evaluation of microsleep. The methods of fuzzy systém and knowledge systém is used. The state of the proband is assessed by classification modules F-COMS and C-COMS which were designed specifically for these systems. The paper also describes the individual frequencies of an EEG spectrum including their mutual dependencies in particular states and individual contributions in a detailed way. The conception of the proposed system for detection and evaluation of the decrease of attention ensues from the uniqueness of an individual, and the inaccuracy of measurement on humans, as well as from the universality of a systém construction, capable of detecting not only the inattention of a driver, but also his/her maximum concentration or pathological changes.