The growth rates, general life-histories and home ranges of two species of rats, Proechimys iheringi and Oryzomys intermedius were studied for 14 months in a Brazilian Atlantic Forest. Relative densities were estimated from mark-recapture data. Weight-age curves were constructed for both species from Von Bertalanffy models fitted to individual growth rates (g/day) on body weight. Both species showed a year-round pattern of reproduction, with no clear peaks for O. intermedius and an increase during the dry season for P. iheringi. The age at first breeding of female P. iheringi was estimated at 8 months and that for O. intermedius, 4 months. Female P. iheringi and O. intermedius annually produced up to 4 and 6 litters, respectively. Size-independent growth rate of both sexes of P. iheringi and female O. intermedius was positively correlated with mean monthly rainfall. The mean density of P. iheringi estimated monthly by the Jolly-Seber method was 5.32 +/- 3.81 ind/ha and that for O. intermedius, 5.27 +/- 1.02 ind/ha. Resident female P. iheringi had home ranges that overlapped little. In contrast, home ranges of resident males overlapped with those of both other males and females. The mean home range size of resident males was larger than that of resident females. Male and female 0. intermedius had home ranges that overlapped little within sexes, but extensively between sexes. The overall results of this study suggest that the mean densities and growth rates of both species of rats are influenced by intrinsic factors such as spacing behavior and extrinsic environmental factors.