To examine how killer-cell immunoglobulin-like receptor (KIR) ligand incompatibilities effect molecular relapse (MR), we compared the occurrence of bcr-abl-positive reverse-transcriptase polymerase chain reaction (RT-PCR) results in 236 CML patients (pts) after human leukocyte antigen (HLA)-identical (n=158) (group 1), HLA class I antigen mismatched and KIR-ligand compatible (n=49) (group 2), and HLA class I antigen mismatched and KIR-ligand incompatible (n=29) (group 3) hematopoietic stem-cell transplantation.