We analyzed changes in gene expression in human colonic carcinoma by fluorescent mRNA differential display. RNA isolated from two samples of normal colon and four cases of colonic adenocarcinoma were amplified with a 15 x 32 set of primers resulting in 2880 cDNAs analyzed with an automated sequencer. Electrophoretic patterns implying constitutive gene expression as well as upregulated and downregulated expression in carcinomas were identified. Forty such cDNA fragments were purified by a novel fluorescent polyacrylamide gel electrophoresis (PAGE)-based method and identified by cyclic sequencing. Most genes showing differential expression were upregulated in colonic carcinoma. Upregulated genes included those for various ribosomal and mitochondrial proteins, heat shock proteins, nucleolar RNA-helicase and phosphoserine aminotransferase. Downregulated genes included histone H3.3. In conclusion, genes associated with vital cellular functions such as transcription, protein synthesis and mitochondrial metabolism were upregulated in colonic carcinoma. Fluorescent mRNA differential display can be applied to the identification of novel cancer-related genes for diagnostic, prognostic and therapeutic purposes.