SUMMARY Mosquito larvae are found in diverse aquatic habitats ranging from freshwater to hypersaline water and must often deal with rapid changes in habitat salinity. We transferred larvae of Aedes aegypti from freshwater to 30% seawater, or vice versa, and measured the time course of changes in their hemolymph ion concentrations, using ion-selective microelectrodes. We also reported the Michaelis–Menten kinetics of Na+ and Cl– transport by the anal papillae for the first time using the scanning ion-selective electrode technique (SIET). Hemolymph concentrations of Na+, Cl– and H+ increased within 6 h, when larvae were transferred from freshwater to seawater and decreased within 6 h, when transferred from seawater to freshwater. Kinetic parameters for Na+ and Cl– transport by the anal papillae were altered after only 5 h following transfer between freshwater (FW) and 30% seawater (30%SW). The Jmax (maximum transport rate) for both ions decreased when larvae were transferred to 30%SW, whereas the Kt (a measure of transporter affinity) increased for Na+ transport but was unaltered for Cl– transport, suggesting that Na+ and Cl– uptake are independent. Data reveal significant changes in ion transport by the anal papillae of mosquito larvae when they are faced with changes in external salinity such that Na+and Cl– uptake decrease in higher salinity. The alterations in Na+ and Cl– uptake may be a consequence of changes in hemolymph ion levels when larvae encounter altered salinity. The rapid changes in ion transport described here compliment the previously observed long term alterations in the morphology and ultrastructure of the anal papillae.