Foucault was interviewed in 1975 for a Brazilian paper:
Q: In your work, the State seems to occupy a privileged place. And the State represents a privileged instance for understanding historical-cultural formations. Could you specify the conditions of possibility which underpin the State?
A: It is true that the State interests me, but it only interests me differentially [différentiellement]. I do not believe that the entirety [ensemble] of the powers which are exercised within a society – and which assure the hegemony of a class, an elite, or a caste in that society – are entirely contained in the State system. The State, with its grand judicial, military and other apparatuses [appareils], only represents a guarantee, the reinforcement of a network of powers which come through different channels, different from these main routes. My problem is to attempt a differential analysis of the different levels of power in society. As a consequence, the State occupies an important place in this, but not a preeminent one (DE no 163, II 812).
“El filósofo responde’, Jornal da Tarde, 1 Nov 1975, pp. 12-13; translated by Plinio-Walder Prado Jr as “Michel Foucault: Les réponses du philosophie”, Dits et écrits text no 163, Vol II, p. 812 (1994 Four Volume edition).
This passage does not appear in the recent reprint of the Portuguese translation of the interview. I guess it must be in the original Portuguese version (which I have been unable to locate) because if not, what is the source for the translation in Dits et écrits? [Update 26 May 2015: the question does appear in the 1975 original – thanks to Andrea Teti for tracking down a copy.]