T-cell dysfunction is thought to be central to the immunodeficiency state seen in patients with the Wiskott–Aldrich syndrome (WAS). Aspects of the WAS phenotype have been corrected in other cell types on introduction of the normal WAS protein (WASP), but the potential for correction of the T-cell defects has not been evaluated. Here we demonstrate that an oncoretroviral vector encoding WASP and green fluorescent protein (GFP), and pseudotyped with the RD114 envelope protein, efficiently transduces primary human T cells derived from WAS patients. Transcription initiated at the oncoretroviral long terminal repeat (LTR) results in levels of WASP that, while lower than those seen in normal control T cells, resulted in correction of the deficient proliferative response to T-cell receptor (TCR) stimulation characteristic of WAS. IL2 secretion after TCR stimulation was partially corrected. Control primary T cells transduced with the same vector responded normally to TCR stimulation, and showed no increase in WASP expression. The demonstration that correction of T cell defects can be achieved by gene transfer supports continued efforts to develop gene therapy for WAS.