The optimal initial volumetric oxygen transfer coefficient (K(L)a) was 60 h(-1) for the production of beta -D-galactosidase from Kluyveromyces marxianus CDB 002, using sugar cane molasses as carbon source. At this K(L)a applying an agitation/aeration relationship of 700 rpm/0.66 vvm resulted in 812 U l(-1) h(-1) for beta -D-galactosidase production. This was about 50% better than a relationship of 500 rpm/2 vvm at the same K(L)a.