The paper examines members' involvement in six trade union organisations. Two of these are relatively large, two are medium-sized, and two are relatively small, In addition, three of the unions can be characterised as ‘white-collar’ and three as ‘blue- collar’. Impressions. are then drawn as to the influence of size, and the broad character of members' work, on the extent and nature of mernbers' participation in this small number of unions. The paper is divided into four sections. The first con siders the importance of members' participation. The second introduces the six trade unions and comments on a variety of factors which appear likely to influence the pattern of members' involvement. The third section investigates the particular experience of members' participation with regard to the reading of union literature, voting in union elections and referenda, and attendance at annual general meetings, mass meetings, and branch and work-place meetings. The fourth section draws some conclusions.