Protein kinases, either membrane-embedded receptorial or cytosolic non-receptorial ones, are important transducers of cell proliferation signals. In almost all tumor cells, the activity of some kinases is deregulated, either because of the presence of cancer-specific aberrant forms, or as a consequence of alterations in regulatory pathways, at the transcriptional or post-transcriptional level, which increase the activity of protein kinases with respect to normal cells. The study of the non-receptor tyrosine kinase Src plays a pivotal role in the field of the molecular genetics of cancer. The Src family of kinases (SFKs) comprises nine members, Src, Fyn, Yes, which are expressed in most tissues, and Blk,Yrk, Fgr, Hck, Lck and Lyn, which are more selectively expressed in particular tissues. To date, cellular (c-) Src has been implicated in the development of human cancer. Like oncogenic v-Src, activated mutants of c-Src can transform cells in culture and induce tumours in chickens. In addition, Src protein expression and/or activity is elevated in epithelial cancers, or cell lines derived from these, and there is often an association with advancement of disease or with malignancy. During the past decade, examples of tyrosine kinases inhibitors have been reported. Many of these compounds were highly active in vitro, but only a few demonstrated in vivo activity. These approaches led to the characterization of the PP1/PP2 derivatives as very strong and selective inhibitors of the c-Src family of kinases. Unfortunately, attempts to improve the biological profile of the latter compounds have so far met little success. Following these studies, some other inhibitors, possessing different chemical structures and interesting c-Src inhibitory activity, have been recently reported. Some of these molecules showed potent inhibition of tumor cell proliferation, which was due to the interference with the signalling pathway at the level of Src tyrosine kinase, providing proof-of-principle for the targeting of Src in anticancer chemotherapy.