The karyotypes and male meiosis of nine Hylidae and one Microhylidae are described. Those are: Hylidae —Hyla raniceps(2n= 24),Phrynohyas venulosa(2n= 24),Hyla crepitans(2n=24),Hyla polytaenia(2n=24),Hyla minuta(2n=30),Hyla rubicundula(2n=30),Hyla nana(2n= 30),Hyla fuscomarginata(2n=24),Hyla trachytorax(2n= 24); Microhylidae —Dermatonotus mülleri(2n=22). Male and female karyotypes are identical. The spermatocytes I of eight species exhibited ring bivalents with terminal chiasmata. Interstitial chiasmata were observed inH. rubicundulaandH. nana.No bivalent suggested by its morphology or behavior the presence of heteromorphic sex chromosomes.