In the accompanying paper we constructed a model for the proliferation and differentiation of granulocyte-macrophage progenitor cells in response to the specific proliferation/differentiation stimulus granulocyte-macrophage colony-stimulating activity (gm-CSA). Here we have tested the model without altering the model parameters, which were estimated on the basis of two types of experiment (clone number versus gm-CSA dose-response curves and clone size distributions with maximal gm-CSA) by using these parameters to simulate additional independent experiments. These included data from separation experiments in which progenitor cells were separated on a basis of their density and were then tested for their sensitivity to gm-CSA and their proliferative capacity. In addition, other sets of experimental data (e.g., mean clone size versus time and colony versus gm-CSA dose-response curves and colony-to-cluster ratios) were also examined to detect whether the mathematical model provides an adequate representation of the data. The model gave a successful simulation of all experimental data.