We have cloned and sequenced a 1.68-kb cDNA encoding arginine kinase in the honey bee, Apis mellifera. The predicted protein shows a high level of identity to known arginine kinases in invertebrates and to other proteins belonging to the conserved family of ATP: guanidino phospho-transferases. The pattern of expression of arginine kinase has been investigated for the first time in various tissues including the brain, antennae and compound eye. Our results show that three isoforms of arginine kinase, transcribed from a single gene, are expressed in a characteristic pattern in major tissues of the honey bee. Arginine kinase mRNA is relatively abundant in the central nervous system and in the antennae. However, the highest level of expression, that is at least two to three times higher than in the brain, is found in the compound eye of the bee. By contrast, the levels of mRNAs encoding another metabolically important enzyme, a-glycerolphosphate dehydrogenase (a-GPDH), are low in the eye. These findings suggest that arginine kinase is an important component of the energy releasing mechanism in the visual system that has high and fluctuating energy demands. Furthermore, our results support the role of phosphagen kinases in energy transport in polarised cells and are consistent with the role of arginine kinase as an energy shuttle that delivers ATP generated by mitochondria to high energy-requiring processes, such as massive membrane turnover and pigment regeneration in the retina.