An arginine auxotrophic mutant strain RN-362 from C. hydrocarboclastus R-7 accumulated a large amount of L-ornithine at the expense of hydrocarbons. The influences of the following factors were studied: arginine concentrations, N sources, C sources, hydrocarbon content and supplement of yeast extract and amino acids. The highest level of L-ornithine accumulation attained after 80-hr. cultivation was about 9 g/li of the culture medium which initially contained 10% (v/v) n-tetradecane as the C source. The maximum yield corresponded to 32.5% (w/w) of n-tetradecane supplied when 1% (v/v) n-tetradecane was added to the medium as a sole C source.