concerned gene is generally available. Under these circumstances, search can be focused on a restricted number of polymorphisms, thus reducing the required number of features on a DNA chip. For instance, diagnostic chips have been prepared to detect mutant alleles in CFTR (cystic tlbrosis), BRCA1 (cancer susceptible gene) and beta-globin. For CFTR, one micro array containing 428 features was designed to detect mutations in exon 11 of CFTR gene and another microarray contained 1480 features for detection of known deletions, insertions or base substitutions. Hybridization of CFTR genomic DNA samples from patients with already characterized mutations gave expected results. Similarly, genotying of patients with un characterized mutations by microarray could be confirmed by techniques of RFLP and PCR. These results confirmed the utility of micro arrays in diagnostics