Gene expression is a noisy stochastic process, since it involves at its core interactions between single molecules: a polymerase and a binding site. However, many biological processes directly dependent upon gene expression are reliable. Prominent among them is morphogenesis: how are body parts so consistently generated and proportioned? In the early embryo, gradients of certain proteins called morphogens affect the pattern of cell differentiation and embryonic development. The variability in morphogen patterns and its effect in the proportions of the embryo has been intriguing biologists for a long time, but the limitations, variability and limited reproducibility of immunostaining of fixed embryos does not allow dynamic measurements. New tools now allow precise measurement of the variability of morphogen patterning in living Drosophila embryos, making it possible to probe the underlying mechanisms of development. ©2007 HFSP Publishing