In this article the spread of demonstrations - a political activity that situates itself in the middle on the scale of conventional - unconventional political action - is studied. The rare survey of the effective participation in demonstrations in Belgium shows that it is rather high. An extensive minority of some 20 to 25% ofthe Belgians declares to have participated in a demonstration. These figures modify the image of the passive, indifferent citizen that research of conventional political participation has shown. The spread of the participation in demonstrations according to age and professional activity, moreover, differs from the pattern found in conventional participation. Demonstrating is typical behaviour of the younger age-categories and therefore of students, but also of farmers, blue collar workers and lower-ranked white collar workers. From this survey follow a number of results connected to the use of demonstrations and the number of demonstrators during the period 1953-74. Related statistics indicate that the number of demonstrations and demonstrators increases, the latter not to the same extent as the farmer however. Furthermore it appears that students, labor unions and agricultural organizations have often come to the streets to enforce their demands. Thematically speaking, particularly problems related to traditional cleavages in Belgian polities have been theobject of demonstrations: ideological, socio-economic and linguistic issues. Organizations active in the area of this cleavages are able to mobilize a great number ofdemonstrators. These organizations are for the most part pillarized and structurally well-developed. Nevertheless the division between issues and organizations during the period 1953-74 has become less unequal. During the sixties and the early seventies the share of traditional cleavages in the number of demonstrations and demonstrators is becoming smaller. New organizations areusing demonstrations more and more to put new issues (environment, foreign policy, quality ofdemocracy, etc.) on the political agenda. They have, however, not the same power to mobilise as do the pillarized organizations.