VIII. To collect leukemia samples prior to transplant and after relapse whenever possible. To assess the overall degree of HLA-class I and class II expression on these paired samples. To test for loss of one or both HLA haplotypes in the relapsed tumor specimens. When observed, to correlate loss of one HLA haplotype with: a) receipt of a transplant capable of targeting only that haplotype; b) establishment of dominance in a 2 haplotype transplant such that the lost haplotype would be the primary target of the dominant donor; c) being the target of the donor predicted to be more alloreactive in a 2 haplotype transplant.