The behavior of colonists on Brazil's Transamazon Highway with respect to felting virgin forest and clearing second growth is modeled as a part of a computer simulation designed to estimate human carrying capacity. Areas cleared are limited by the resources available to the colonists, land, labor, and capital. Input parameters for the simulation are based on interviews conducted with colonists in a study area located 50 km west of Altamira, in the State of Pará. Data from the Ouro Preto Colonization Project in the State of Rondônia show many similarities with the patterns observed in Altamira, for purposes of simulation, areas available to colonists in their tots are classed by age of second growth, with a separate class for virgin forest (not previously felted by colonists) . The probability of clearing each class is calculated based on data representing the proportion of lot-years in which the class was present, and was cleared. The probabilities are for clearing some part of the area of the class in question; these "clearings" are preparations of land for crops other than pasture (pasture, is calculated separately] . in Rondonia, cleared areas in lots occupied by a single owner increase linearly for about six years, after which a plateau is reached. Lot sales to newcomers lead to renewed periods of rapid clearing. The relations of clearing behavior to carrying capacity include: (a) the lack ofa fallowing schedule with uncultivated periods sufficient to restore soil quality, such as those in traditional systems of shifting cultivation, can potentially lead to degradation and lowering of carrying capacity, (b) rapid deforestation leads to the planting of pasture, which is linked to low human carrying capacity, and (c) exceeding a maximum limit for felling can be taken as one of the criteria for determining carrying capacity.