Assessment of risk factors for acute graft-versus-host disease (aGvHD) might help in tailoring the intensity of prophylactic immunosuppression after allogeneic stem cell transplantation (SCT), thereby decreasing the relapse rate in leukaemia patients. In this study, we analysed whether the number of recipient blood T cells and plasma levels of different cytokines were correlated with the risk of aGvHD after allogeneic SCT. Analyses were performed in 23 patients receiving pSCT immediately before or during the first 2 days of the conditioning regimen. In all, 40 or more Tc-1 cells/microl pretransplant were associated with a significantly increased risk of aGvHD (10/10 patients with GvHD>/=II; 4/13 patients without aGvHD with a Tc-1 number >40/microl, P<0.002, Fisher's exact test). In addition, 40 or more Th-1 cells/microl pretransplant were also associated with a significantly increased risk of aGvHD (P<0.04, Fisher's exact test). Furthermore, the number of Th-2 cells was significantly higher in patients with severe aGvHD even though the median absolute cell counts were very low. However, all other investigated parameters did not reveal predictive value. In conclusion, determination of T-1 cells prior to SCT might determine patients with high/low risk of aGvHD and could thus be used to control immunosuppression after SCT.