P94fer is a ubiquitous, nuclear and cytoplasmic tyrosine kinase, whose accumulation has been demonstrated in all mammalian cell lines analysed. In the present work, the p94fer expression profile was determined in cell lines which were not tested before. While being present in several hematopoietic and non hematopoietic cell lines including thymic stromal cells, the p94fer kinase could not be detected in pre-T and T cell lines. p94fer was also absent in pre-B line, but accumulated in these cells upon their induced development to antibody producing cells. This is in agreement with the absence of p94fer in primary thymic and splenic T lymphocytes and its induced accumulation in stimulated B cells. Relatively high p94fer levels were detected in primary thymic and splenic stromal cells. Ectopic expression of p94fer in pre-T cells slightly affected their cell cycle profile but it did not affect their apoptotic death which was induced by ionizing radiation. However, p94fer facilitated dramatically, the cellular recovery of gamma irradiated pre-T cells which have escaped the apoptotic death. The enhanced recovery of the irradiated, p94fer expressing pre-T cells, resulted most probably from their increased survival, rather than from a prominent change in their proliferation rate. The absence of p94fer from pre-B and pre-T cells, may thus contribute to the relative sensitivity of these cells to ionizing radiation and to their dependence on the functioning of other nuclear tyrosine kinasese.