A comparative study of shaken flask cultures of some yeast strains capable of fermenting lactose showed no significant differences in EtOH [64-17-5] yield among the 4 best strains. Use of whey permeate concd. 3 times did not affect the yields. An optimal growth temp. of 38 Deg was detd. for Kluyveromyces fragilis NRRL 665. Elemental anal. of both the permeate and the dry cell mass of 2 strains indicated the possibility of a stoichiometric limitation by nitrogen. Batch cultures in lab. fermentors confirmed this finding and revealed, in addn., the presence of a limitation due to growth factors. Both types of limitations could be overcome by adding yeast ext. The max. productivity of continuous cultures could thus be improved to 5.1 g/L-h. The max. specific growth rate was ~0.310 h-1. [on SciFinder (R)]