A new isolate of Mortierella alpina, &# 62;98% identical with M. alpina ATCC 16266, was cultivated in a defined glucose-based medium with three organic nitrogen sources (glycine, urea and Na-L-glutamate) at three different concentrations in shaking flasks at 20 degrees C. The results were compared to the cultivation in complex medium with yeast extract as nitrogen source. In the defined media, high yields of polyunsaturated fatty acids (PUFAs) and arachidonic acid (ARA), respectively, were obtained with Na-L-glutamate. However, the absolute highest yields of PUFA and ARA were measured with the yeast extract medium. An optimized yeast extract complex medium was used for a submerse bioreactor cultivation in a 45-L scale. Furthermore, M. alpina was cultivated in a solid state fermenter, using an oat bran water mixture as substrate.