Karyotypes of ten species of Brazilian rodents, collected in the State of Sao Paulo are presented:Akodon (Thaptomys) nigrita nigrita(2n= 52);Zygodontomys lasiurus(2n= 34);Thomasomys (Delomys) dorsalis collinus(2n= 82);Oxymycterus sp1.andOxymycterus sp2.(2n= 54);Calomys sp.(2n= 66);Clyomys laticeps laticeps(2n= 34);Euryzygomatomys guiara(2n= 46);Proechimys iheringi iheringi(2n= 62, 64) andEchimys sp.(2n= 90).