NOVELTY - Triggering triacylglycerols accumulation in microalgae comprises inhibiting the sterol metabolism.    USE - The methods are useful for triggering triacylglycerols accumulation in microalgae; producing fatty acids, biofuels, pharmaceutical or cosmetic compositions, and food supplements. The inhibitor of sterol metabolism is useful for accumulating triglycerides in microorganism, preferably in microalgae (all claimed).    ADVANTAGE - The main advantages of microalgae in relation to plants for the production of triacylglycerol are the following: (a) this bioresource does not compete with the agro-resources used for animal or human nutrition; (b) algal growth can be monitored in controlled and confined conditions in an environmental friendly process using recycled inorganic and organic wastes generated by other human activities and the use of microalgae allows trapping and converting industrial byproduct gases (e.g. carbon dioxide (CO2)) into valuable organic molecules; (c) the algal biomass productivity is high, microalgae showing a very high potential of productivity with cost savings when compared to land plants, where their yield is variable and determined by the culturing approach employed: it is relatively low in open pond systems while it can be significantly increased in closed photobioreactors where culture parameters can be controlled; and (d) this bioresource does not depend on a geographical location, or on a season.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method for producing fatty acids comprising a triggering of triacylglycerols accumulation step in microalgae;    (2) a method for producing biofuels comprising a triggering of triacylglycerols accumulation step in microalgae, and a subsequent trans-esterification step of the obtained triacylglycerols;    (3) a method for producing pharmaceutical or cosmetic compositions comprising a triggering of triacylglycerols accumulation step in microalgae; and    (4) a method for producing food supplements comprising a triggering of triacylglycerols accumulation step in microalgae.