The nm23-H1 gene has been suggested to be a metastasis suppressor gene. Studies about the events of loss of heterozygosity (LOH) at the nm23 locus and its correlation to metastasis are controversially discussed. To optimize detection of LOH at the nm23 locus, we screened two P1 clones for additional microsatellites. Tumor and normal DNA from 37 colorectal, 16 gastric, and 8 germ cancer patients were examined for LOH. We found two new CA repeats, one 5' to nm23-H1 and another 3' to nm23-H2. Using these nm23 locus-specific CA repeats and five other chromosome 17 loci (D17S1522, D17S1566, D17S855, D17S515, and TP53), allele loss was observed in 4/32 (12.5%) patients with colon cancer, 2/14 (14.3%) with gastric cancer, and 1/7 (14%) with germ cancer. No isolated LOH of the nm23 region was observed.