A mammalian homology of Drosophila Disabled protein has been identified and cloned. In particular, the murine homolog designated mDab1 has been cloned and expressed. mDab1, when tyrosine phosphorylated, binds to the SH2 domain of Src, Abl and Fyn. Antibodies specific for mDab1 are provided as are methods for the screening of agents for their ability to modulate mDab1 activity. Methods for diagnosing Disabled protein associated disease are also provided.