SummaryDifference in gene expressions is characteristic of the function of different cell types and those genes with low expression variance can be used as standards for quantitative gene expression studies. Microarray technology is used to study global gene expression within a cell; hence, represents a suitable source of data to mine for genes with low expression variance. The coefficient of variation (COV) of each gene was determined and a threshold of less than 0.1 COV was used to select stably expressed genes in each data set. Our results showed that microtubule affinity-regulating kinase 3 (MARK3) has the lowest COV in eight microarray datasets. In addition, the gene expression of housekeeping genes, which is very likely to be stably expressed, tends to fluctuate highly under different conditions, marking them as being less reliable for use as reference genes.