The objective of this retrospective study was to evaluate the role of MICA in heart graft acceptance. Pre- and post-transplant sera from 31 patients were evaluated for MICA antibodies by cytotoxicity on recombinant cell lines and soluble MICA (sMICA) concentrations by ELISA. The results demonstrated that the patients with post-transplant anti-MICA antibodies were at a high risk for the development of severe acute rejection (AR) (p<0.03; OR=8.5). However, the presence of post-transplant sMICA was found to be associated with functioning grafts without AR episodes (p<0.03, OR=7.9). In this preliminary survey, the negative association of sMICA with AR was found to be in the absence of MICA antibodies. Further research is needed to clarify the role of sMICA in allograft acceptance. Post-transplant evaluation of humoral immune response to MICA and the measure of sMICA in patient's sera may provide a good predictor of AR.