The introduction of novel targeted therapies into the clinic in recent years has had a considerable impact on the management of several neoplastic diseases--such as gastrointestinal stromal tumors, hepatocellular carcinomas and renal cell carcinomas--considered until recently refractory to systemic therapies. We describe here two such novel biological agents, sunitinib and sorafenib, as a paradigm of the successful clinical application of new concepts. Sunitinib and sorafenib are small molecule tyrosine kinase inhibitors that target vascular endothelial growth factor receptor, platelet-derived growth factor receptor, C-Kit and others. Both agents are administered orally; sunitinib is tyically given in cycles for 4 consecutive weeks with 2 weeks off, while sorafenib is given continually. Side effects occur in most patients, similar for both agents; they may affect several systems and organs but are mostly mild and easily manageable, rarely requiring discontinuation of the drug. However, these toxicities mandate prompt attention and intervention. The most frequently observed effects are hypertension, nausea, anorexia, asthenia and cutaneous manifestations; cardiac abnormalities may include congestive failure. Sunitinib, and markedly less frequently sorafenib, may cause thyroid gland dysfunction, mainly hypothyroidism. Antitumor activity has been shown for renal cell carcinoma in pivotal trials, for sunitinib as first-line treatment and for sorafenib in previously treated patients as second-line. Sunitinib is now approved as second-line therapy for patients with GIST refractory to imatinib; sorafenib has resulted in a significant prolongation in median survival in patients with hepatocellular carcinoma. Ongoing clinical trials will further define the spectrum of these agents' antitumor activity, their role in combination with other drugs, as well as their optimal dose and schedule of administration.