On the basis of all hitherto known P450 X-ray structures and applying standard homology modelling procedures a three-dimensional model of the lanosterol-14 alpha-demethylase active site was constructed. The modelled active site nicely hosts the natural substrate lanosterol and the substrate-enzyme complex displayed stability in a 70 ps molecular dynamics simulation. The importance of Thr 122 of lanosterol 14 alpha-demethylase for hydrogen bond formation with the 3-hydroxyl group of lanosterol was found to be a characteristic feature of the interaction geometry.