Vertebrate T cells express either an αβ or γδ T cell receptor (TCR). The developmental relatedness of the two cell types is unresolved. αβ⁺ T cells respond to specific pathogens by collaborating with immunoglobulin-producing B cells in distinct lymphoid organs such as the spleen and Peyer's patches. The precise influence of αβ⁺ T cells on B cell development is poorly understood. To investigate the developmental effects of αβ⁺ T cells on B cells and γδ⁺T cells, mice homozygous for a disrupted TCRα gene were generated. The homozygotes showed elimination of αβ⁺ T cells and the loss of thymic medullae. Despite this, γδ⁺ T cells developed in normal numbers, and there was an increase in splenic B cells.