Carrier ampholytes (CAs), originally designed for isoelectric focusing (IEF), have been used as background electrolytes (BGE) in capillary zone electrophoresis (CZE). Their main electrophoretic properties, relatively high buffering capacity and low electric conductivity allowed fast (less than 2 min) and high efficient (500,000 theoretical plates/m) separation of a test mixture of proteins under very high electric field strength (more than 1000 V/cm). The results obtained in such buffers have been compared to those obtained in more classical sodium--phosphate and sodium--N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonate) background electrolytes. High ionic strength classical buffers were necessary to achieve the separation of the proteins contained in the test mixture. This induced a significant Joule heating and temperature increase inside the capillary whereas a negligible Joule heat was produced in carrier ampholyte buffers even at the above electric field strength (higher than 1000 V/cm).