The cellular chemical machinery controlling all living processes is mediated by macroassemblies of enzymes and nucleic acids. These complexes form, break up in different orders and reorganize in ways that result in the chain of events that we call a biochemical 'pathway'. However, all of the methods available to study protein interactions in living cells allow only the observation or recreation of binary complexes. Two recent reports and earlier studies describe the use of chemical 'dimerizers' that can dynamically induce assembly or disassemby of protein complexes. The dimerizer tools create the opportunity to understand the 'real' biology of macromolecular assembly.