Metal pollution of aquatic ecosystems is a problem of economic and health importance. Sensitive molecular biomarkers of metal exposure are sorely needed. We have isolated a cDNA from the midge Chironomus tentans that is transcribed in all organs and developmental stages. The cDNA encodes a protein, designated Chironomus tentans alpha-tubulin 1 (CTTUB1), which has significant similarities with invertebrate and vertebrate alpha-tubulins. CTTUB1 is abundantly transcribed in embryos and to a lesser extent in adults and larvae. CTTUB1 RNA and protein abundances are increased in larvae exposed to copper or cadmium. The pattern of cellular distribution of CTTUB1 protein in the midgut epithelial cells was radically affected by cadmium. In the midgut cells of unexposed larvae, CTTUB1 was found evenly distributed throughout the cytoplasm, while in cadmium-exposed larvae, CTTUB1 was mostly concentrated along the basolateral plasma membrane. A mechanism for the regulation of alpha-tubulin synthesis by cadmium is proposed. This is the first report on the isolation of a metal responsive gene from a neartic aquatic insect.