Abstract B cell receptor (BCR) stimulation induces phosphorylation of a number of proteins, leading to functional activation of B lymphocytes. Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase, involved in a variety of signaling pathways. In this study, we show that FAK is tyrosine-phosphorylated and activated following BCR stimulation. We also demonstrate constitutive association of FAK with the Src-family kinase Lyn and with components of the BCR. Association of Lyn with FAK which was not correlated with BCR-induced activation of both kinases, appeared to be mediated via the binding of Lyn to the COOH-terminal part of the FAK molecule. Our results indicate that FAK is a component of the BCR complex and that it participates in BCR signaling.