Receptor (RTK) and nonreceptor (NTK) protein tyrosine kinases play a central role in trans- duction of extracellular signals, both in normal and neoplastic cells. Therefore, several approaches to inhibit PTKs have been developed. According to the structure of natural protein kinase inhibitors (quer- cetin, erbstatin ) Levitzki and coworkers prepared first synthetic tyrosine kinase inhibitors and coined the term tyrphostins (tyrosine phosphorylation inhibitors). Over 30 tyrphostins are now in various stages of clinical development. The structure, biological properties and antitumor activity of selected receptor tyrosine kinase inhibitors (EGFRs, IGFRs, VEGFRs) and nonreceptor kinase BRC-ABL are discussed. The recent results indicate, that most effective therapy may be administration of the combination of PTK inhibitors with other signal transduction inhibitors or cytostatics.