Optimum conditions for cultivation of Mortierella ramanniana mutant MM 15-1 were investigated with an aim of producing a lipid which contains high gamma-linolenic acid (GLA). The optimum initial glucose concentration and pH control level were 300 g/l and 4.0, respectively. Although both pellet and filamentous forms of this mutant were observed during the cultivation, the pellets accumulated lipid with higher GLA content than the filamentous forms. The effects of culture conditions on pellet formation were therefore investigated in a 30-l jar fermenter. The results showed that with an inoculum spore concentration of 5.0 x 10(3)/ml and an agitation speed of 800 rpm, 0.15-0.5 mm pellets were formed and consequently, the GLA content of the lipid increased to a very high value of 18.3%. Furthermore, when this process was scaled up to a 10-kl fermenter, using the impeller tip velocity as the scale-up parameter, both the pellet formation and the lipid production as well as the GLA content of the lipid were consistent with those obtained in the 30-l jar fermentor.