BACKGROUND: Enzymatic esterification of phytosterols with fatty acids from butterfat in equimolecular conditions to produce phytosteryl esters was performed in solvent-free medium. Commercial and immobilized Candida rugosa lipases were used as biocatalysts for the reaction. RESULTS: By this methodology, under simple and mild reaction conditions (without solvents, 50 degrees C and short reaction times), 94% and 99% (w/w) of phystosteroyl esters were obtained in 48 h and 9 h with the commercial and the immobilized lipase, respectively. The effects of temperature, fatty acid specificity, enzyme amount and residual activity of each lipase were also evaluated. CONCLUSIONS:The phytosteryl esters from butterfat produced in this study are expected to have lower melting point, improved oil and fat solubility and bioavailability compared to that of their corresponding free phytosterols. (C) 2008 Society of Chemical Industry