DNA microarray technology has permitted large scale parallel analysis of gene expression of several diseases, including cancers. Real-time PCR has become a well-established procedure for
quantifying levels of gene expression. We evaluated Real-Time PCR to validate differentially expressed genes identified by DNA arrays. Gene expression of three different grade of transitional cell carcinoma (TCC) of human bladder cancer was determined using microarray slide containing cancer-related genes. Data obtained were sorted according based on the ratios between Cy3 and Cy5 dyes used and revealed 119, 235 and 183 differentially expressed genes in TCC WHO Grades I, II and III, respectively. Real-time PCR used SYBR Green-1 dye detection to validate relative change in gene expression. Real- Time PCR confirmed the change in gene expression of 17 of 28 (75%) genes identified by microarray. Real-Time PCR also suggest that genes identified by microarray with two or higher fold change cannot be eliminated as false nor be accepted as true without validation. Real-Time PCR based on SYBR Green- 1 is well-suited to validate DNA array results because it is quantitative, rapid and requires less RNA compared to the conventional assays.