S-Adenosyl-L-methionine (AdoMet) was produced by a mutant strain Kluyveromyces lactis AM-65 grown on whey. A full factorial design method of three factors - (NH4)(2)SO4 (factor x(1)), corn steep liquor (factor x(2)) and l-methionine (factor x(3)) on three levels - was used to determine the optimal medium conditions for the production of AdoMet. A time course shake-flask experiment in optimal whey medium (x(1)=3.1 g l(-1), x(2)=12.7 g l(-1), x(3)=4.6 g l(-1)) was also carried out and the results confirmed the results of the factorial design and subsequent quadratic modelling and optimization of AdoMet production which reached 90 mg g(-1) cell dry wt.