Current microarray analysis uses 'chips' containing either 25-residue oligonucleotides synthesized by photolithography or cDNAs placed by robotic spotting. In the April Nature Biotechnology, Hughes et al. describe a microarray technique that exploits an ink-jet printing method and standard phosphoramidite chemistry (Nature Biotechnology 2001, 19:342-347). The ink-jet synthesizer can deliver 25,000 phosphoramidite-containing microdroplets to a 25 x 75 mm glass slide. Hughes et al. examined a large range of parameters to define conditions for optimized specificity and sensitivity. They found that 60-mer oligonucleotides hybridized at 30-32% formamide gave the best results. The absolute detection limit was approximately 0.1 copies per cell equivalent. The ink-jet arrays were as effective as spotted cDNA microarrays. Moreover, Hughes et al. report that single carefully chosen 60-mer oligonucleotides can be preferable to arrays containing multiple oligonucleotides or cDNAs as they offer maximal specificity. The ink-jet technology provides a very flexible...