Phenotypic analysis showed a significant increase of CD3+/CD57+ lymphocyte subpopulation in 88 kidney-transplanted patients when compared with non-transplanted patients. No clear correlation was found between the increase of this cell subpopulation and renal function, immunosuppressive regimen, and allogenic or viral stimuli, when each of these factors was considered. Conversely, there was a significant correlation between the proportion of CD3+/CD4+/CD57+ cells and the post-transplant follow-up period. Finally, functional study of CD3+/CD57+ cells suggested that they have suppressive properties, in vitro.