Analyzing the putative interaction partners of an individual protein is one approach to elucidate its function. In the LuMPIS protocol, bait and prey proteins are expressed with N-terminal maltose binding protein (MBP)- and eGFP-luciferase (eGFP-luc) tags, respectively. Positive protein-protein interactions (PPIs) can be detected after pull-down of the MBP-tagged prey protein using amylose beads followed by the bioluminescence detection of the bound eGFP-luc-tagged bait protein. The LuMPIS technology offers the following advantages: the PPIs are detected in the mammalian cell context, the use of two long protein tags (i.e., MBP and eGFP-luc) increases the expression levels of genes whose gene expression levels are known to be frequently impaired, the use of amylose beads for pull-down is much more economic as compared to sepharose beads in combination with monoclonal antibodies and finally, the use of an eGFP-luc-tag enables the qualitative control of transfection efficiencies by fluorescence microscopy prior to starting the assay.