Multicellular organisms, particularly their immune systems, rely on complex cell-to-cell communication, mediated by signalling molecules that form spatiotemporal concentration gradients. Here, high-throughput microfluidic cell culture and fluorescence microscopy, together with quantitative gene expression analysis and mathematical modelling, have been used to investigate how mammalian cells respond to different levels of TNF-? and signal to NF-?B. Both digital and analogue responses are revealed.