On page 1001, Lindblad-Toh et al. demonstrate that single-nucleotide polymorphism (SNP) array hybridization is an accurate and efficient approach for evaluating genome-wide tumor loss of heterozygosity (LOH). The strategy uses 24-multiplex PCR reactions to amplify polymorphic regions from tumor samples, followed by hybridization to a human SNP chip to determine the genotypes for nearly 1,500 genome-wide markers. The results are then compared to genotypes obtained from nontumor samples from the same individuals. The authors demonstrate that the microarray-based approach offers advantages in throughput relative to other methodologies, by decreasing the amount of sample required and an increasing the number of loci studied.