Biochemical studies on ecdysteroid metabolism in arthropods suggest that aldoketoreductase enzymes (AKRs) may be involved in this pathway, but very few molecular data are available on these oxidoreductases in invertebrates. Looking for such enzymes in the crayfish Orconectes limosus, we have used a PCR strategy with primers deduced from a recent insect 3 beta -reductase sequence, and from mammalian BP-reductase sequences. A full-length cDNA, corresponding to a putative AKR, was isolated from crayfish antennal gland. This cDNA contains an open-reading frame of 1008 bp, encoding a predicted protein of 336 amino acids. Northern blots indicated a restricted expression of the transcript in the antennal glands, quite constant during the molting cycle, and in situ hybridization demonstrated a strong expression of the transcript in the labyrinth. This is to date the first member of the AKRs superfamily characterized in a crustacean species, and the putative function of the corresponding enzyme is discussed.