This article adresses an original experience of adult education during the "Front Populaire". The broadcast lectures of the Centre Confédéral d’Education Ouvrière (CGT's working-class education confederal center) are often cited though scarcely studied. Created in 1933 as a democratisation tool ok knowledge, the CCEO has the opportunity in 1937 to access to a mass media as to enlarge its audience. This article proposes to underline how, during three years through "la voix de la CGT", the trade-union acquired skills regarding the special demand of a broadcast programm. During all this period, it tried both to fulfill its mission of education and struggle against a strong propagandist temptation.