We investigated whether the src‐family tyrosine kinase Lyn is involved in the generation of interferon α (IFNα) signals in haemopoietic cells. In vitro kinase assays using IFNα‐sensitive cells of B‐cell origin demonstrated the presence of IFNα‐dependent kinase activity in anti‐Lyn immunoprecipitates. Further studies demonstrated that Lyn associates via its src homology 2 (SH2) domain with the Janus family tyrosine kinase Tyk‐2. This interaction was IFNα‐dependent and involved direct binding of the SH2 domain of Lyn to the IFNα‐activated form of Tyk‐2. Thus, during binding of IFNα to its receptor in malignant haemopoietic cells, Lyn is engaged in an IFNα‐signalling pathway, probably downstream of Tyk‐2.