Abstract. Pattern formation in development is a complex process that involves spatially-distributed signals called morphogens that influence gene expression and thus the phenotypic identity of cells. Usually different cell types are spatially segregated, and the boundary between them may be determined by a threshold value of some state variable. The question arises as to how sensitive the location of such a boundary is to variations in properties, such as parameter values, that characterize the system. Here we analyze both deterministic and stochastic reaction-diffusion models of pattern formation with a view toward understanding how the signaling scheme used for patterning affects the variability of boundary determination between cell types in a developing tissue.