I do not speak except to those capable of hearing me.
That de Sade used the word entendre - to hear - rather than comprendre - to understand - may confuse scholars who encounter this sentence. That he would have had no patience for the small-minded makes sense - de Sade certainly had some controversial opinions for his time and place, but to specify hearing certainly mixes things up a bit. Perhaps in this case a literal translation is not best, and his intent may well have been that he ignores those who cannot at least respect his beliefs. (thbz reports that entendre used to mean "understand" in French, like the Spanish verb entender, and that the usage has changed over the years to the present "hear" meaning.)
I have found that the full text of this quote is: "Je ne m'adresse qu'à des gens capables de m'entendre, et ceux-là me liront sans danger." The source is http://www.republique-des-lettres.com/s1/sade.shtml which is entirely in French. As it has been a few years since I studied French literature I am reluctant to complete the translation.
An update, late February 2004...
I was going through my nodecount and came across this one, and couldn't remember what I'd written for it. Reading over that final quote again, I think I have a somewhat complete translation: I am addressing only those people who are able to understand/hear me, and those people can read my writings without danger. I base this translation partly on a knowledge of de Sade's writing topics, and I also admit that the last part, "without danger," may be open to interpretation based on de Sade's themes.