The CELL NUMBER REGULATOR/FW2.2-like (CNR/FWL) gene family was named in reference to its founding member, the FW2.2 gene (standing for Fruit Weight QTL on chromosome 2, number 2), which underlies the major quantitative trait locus (QTL) governing fruit size in tomato. The CNR/FWL gene family encompasses hundreds of related sequences in the plant, animal, and fungal reigns (Guo et al., 2010), with a large diversity in protein size ranging from a hundred to several hundred amino acids. In the present study, we aimed at investigating whether SlFWLs proteins play a role in the control of organ growth in tomato and shed light on the critical involvement of SlFWL5 in leaf development. Here we performed a co-immunoprecipitation experiment on protein extract from tomato leaves (leaves 3 and 4 of 6 weeks old plants) from wild-type and 35S::SlFWL5-YFP Ailsa Craig plants in order to identify interacting proteins of SlFWL5.