Specificity of hybridization was determined in the hexaplexed assay (A) and the icosaplexed assay (B). Oligonucleotides representing 20 genes were coupled to 20 different color-coded microspheres. Various amounts of the complementary target oligonucleotides tagged with biotin were mixed in four tubes as indicated in Table 2. NTSR served as a negative control in the experiment. (A) Only the first six targets (see Table 2) and their corresponding capture-probe-coupled microspheres were added to the assay. (B) All 20 targets and their corresponding capture-probe-coupled microspheres were added to the assay. In both experiments A and B the background fluorescence of each set of microspheres was subtracted.