The efficacy of bone marrow transplant (BMT) T-cell depletion for the prevention of acute graft-versus-host disease (GVHD) has been demonstrated in animal models and in clinical studies. The importance of T-cell depletion has to be evaluated with standardized methods suitable for routine purposes. We report herein an in vitro mature T-cell depletion using a cocktail of three monoclonal antibodies (CD2, CD5, and CD7) and baby rabbit complement in 38 histocompatibility leucocyte antigen (HLA)-identical BMT with no more than grade II acute GVHD. The T-cell depletion was quantified using three prestandardized immunological methods: immunofluorescence (IF) analysis, SRBC-rosetting assay, and PHA proliferation assay. A mean of 97.5% IF-assessed T-cell depletion was achieved in the 38 BMT. The immediate IF analysis using three distinct sets of anti-T-cell monoclonal antibodies allowed us to detect a mean of 1.2% residual T cells. The SRBC-rosetting assay was not useful to quantify T-cell depletion because no residual SRBC-rosette-forming cells could be detected in every case. The results of a prestandardized PHA-induced proliferation assay gave a mean 96.7% inhibition of proliferation, and they were correlated with the IF results although the IF threshold of detection was higher. From these data we conclude that our in vitro T-cell-depletion procedure is reproducible and that standardized simple immunological methods such as immediate immunofluorescence analysis and PHA proliferation assay provide good tools to assess a T-cell depletion effective in the prevention of acute GVHD.