The growth of the filamentous fungi Geotrichum candidum and Penicillium camembertii on peptones as a sole carbon and nitrogen source, and in the presence of a second carbon source, lactic acid, have been compared. On both media, G. candidum exhibited similar kinetics until the end of growth, since it preferentially metabolized peptones as a carbon source, and lactic acid only for cellular maintenance during stationary phase. Growth of G. candidum was then nitrogen limited (peptones). On the contrary, fewer amino acids were convenient carbon sources for P. camembertii, resulting in a simultaneous consumption of peptones and lactic acid, and a cessation of growth due to the complete consumption of lactic acid. Morever, a lower amount of ammonia was produced since this metabolite resulted from the deamination of only carbon and nitrogen source amino acids. The production of ammonia induced an alkalinization of the broth (from 4.5 to 7.1). Morever, it was demonstrated that lactic acid consumption contributed also to media alkalinization (final pH 8.4). In absence of lactic acid, the medium contained a lower amount of available carbon, resulting in the absence of stationary state, deceleration growth phase was immediately followed by the death phase.