Attention is drawn to the development of a new and green alternative technique for the extraction of essential oil from citrus peels. The process uses the hydro-diffusion phenomenon generated by microwaves to extract essential oil from the inside to the outside of the biological material and gravity to collect and separate them. The present apparatus permits fast and efficient extraction, reduces waste, avoids water and solvent consumption, and allows substantial energy savings. (C) 2008 Elsevier Ltd. All rights reserved.