New solvent systems for the extraction of erythromycin were studied in which octanol was used as the extractant instead of butyl acetate. The mechanism for these new extraction systems is not simple physical distribution but the formation of a neutral complex of erythromycin. A neutral extraction complex formed between the neutral molecules of erythromycin and extractant by hydrogen bonding, and the formed neutral extraction complex moves into the organic phase. Extraction reaction equations and mathematical models of extraction equilibrium and re-extraction equilibrium are proposed for these new extraction systems. Experimental results show that the new extraction systems offer technological and economic advantages owing to the low solubility of the extraction solvents in the aqueous phase. The solvent consumption of the new extraction process was less than 3kg per billion active units compared with 9-10 kg per billion active units for a butyl acetate extraction system. In addition, the recovery of solvent from raffinate may be eliminated, thus reducing energy consumption. (c) 2005 Society of Chemical Industry.