Summary1. Techniques are described for producing purified brush‐border membrane vesicles (BBMV) of crustacean hepatopancreas which can be used to examine the characteristics of solute transport at the apical pole of hepatopancreatic epithelial cells.2. Hepatopancreatic BBMV illustrated Na‐dependent, carrier‐mediated sugar transport which was electrogenic and sensitive to pH. Increased proton concentration lowered the Michaelis‐Menten constant for glucose transport and increased the apparent diffusional permeability of the membrane to sugar.3. Transports of L‐alanine and L‐lysine by hepatopancreatic BBMV were Na‐independent, carrier‐mediated, and strongly sensitive to transmembrane electrical potential after protonation at acidic pH. L‐alanine and L‐lysine were competitive inhibitors of each other for influx into BBMV and also illustrated trans‐stimulation, suggesting that both amino acids use the same transfer mechanism. L‐Leucine was a non‐competitive inhibitor of L‐lysine influx and may employ a distinct Na‐independent transport process.4. L‐glutamate transport after protonation at acidic pH was Na‐dependent, suggesting that a different transport mechanism was responsible for its movement across hepatopancreatic BBMV than that facilitating the transfer of alanine or lysine.5. Preliminary experiments indicate the presence of Na/H antiport in hepatopancreatic BBMV, providing, for the first time, a possible mechanism for gastrointestinal luminal acidification in crustaceans.6. A proposed model for nutrient transport by crustacean hepatopancreatic BBMV is presented which suggests that transapical transfers of both sugars and amino acids are strongly influenced by in vivo luminal acidification. Luminal protons have at least two major effects on nutrient transport in these animals: (a) titration of sugar transport proteins with subsequent stimulatory effects on influx kinetic constants; (b) protonation of luminal amino‐acid‐charged moieties and conversion into appropriate substrates for transport by either Na‐dependent or Na‐independent, memb