The study deals with the problems of knowledge synthesis at the secondary stage of general education with regard to the required qualities of present-day complete secondary education. It proceeds from the Marxist conception of education and its function in the development of society and the individual. The conception of the didactic from of the knowledge synthesis is derived from the teoretical analysis of the problem: it is a question of a purposeful teacher-controlled process of forming the conceptual knowledge system in the pupil and at the same time developing the ways of the application of the knowledge by pupils. The study gives the results of an empirical research into the knowledge synthesis, carried out at all types of secondary schools in the field of general education. The methods of finding out the aspects of the knowledge synthesis is a set of problem assignments for the pupil. The appropriateness of this method is manifested especially in the fact that the solution of assignements by pupils make it possible to follow the width and ways of the pupils’ thinking about problems. The quantitative and especially qualitative analyses of the results of the research have brought the following findings: The investigated aspects of the knowledge synthesis and thus also the application of knowledge at a certain theoretical level are still limited as far as the knowledge of secondary schools pupils is concerned. In most cases the pupils’ knowledge gets stuck on the level of fragmentary experience without the pupils being able to generalize the individual concrete facts and to interpret them in contets. The investigated aspects of the knowledge synthesis in the field of general education are, for the time being, apparent to a greater extent among senior high school (grammar school) pupils. The value of the research in question can be seen in the fact that it draws attention to some unused possibilities in the realization of secondary education at various types of secondary schools.