We have developed a procedure of covalently attaching nucleic acids to 1"×3" glass microscope slides. When we calculate the degree of target wash-off during hybridisation and subsequent washes (using oligonucleotides of 35nt to 45nt in length), we demonstrate a very stable attachment of the target nucleic acid to the glass slide. We measured the target wash-off using our chemistry and compared it to target wash-off experiments with published poly-L-lysine, aldehyde, UV crosslinking and amino chemistries. Our chemistry exhibits almost no wash-off whereas the other chemistries can exhibit as high as a 70% wash-off. We also wished to investigate different types of target nucleic acids on microarrays. Using our developed chemistry, we chose 96 yeast genes regulated during auxotrophic shift and designed and made three different types of target nucleic acids to be attached to microarrays. We made full-length cDNAs (500nt–2000nt), optimised amplified gene segments (400nt) and specific oligonucleotides (35nt–45nt) for comparison. These microarrays were hybridised to fluorescently-labeled cDNA made from yeast mRNA and the hybridisation signals were determined using a laser scanner. These experiments are designed to determine the relative sensitivity and reproducibility of these types of nucleic acid targets in gene expression experiments. The results of these experiments will be discussed.