In the ‘pre-history’ of Argentina's labour movement lie the mutual-benefit societies. Although these associations embraced almost half of the workers of Buenos Aires at the time of the Centenario (1910) little is known about them. The article explores the main parameters shaping the development of the mutual benefit societies, their relationship to the immigrant communities and their role in relation to social security. It traces, finally, the ambiguous relationship between the mutual benefit societies and the emergence of Peronist trade unionism in the mid-1940s.