The results of studies with the microalga Haematococcus lacustris, grown under heterotrophic, autotrophic and mixotrophic conditions, were employed to fit kinetic parameters such as specific growth rate, linear growth rate and acetate consumption as a function of irradiance and acetate concentration. Growth was inhibited at the highest light intensities used, as was acetate uptake. The specific growth rate in mixotrophic conditions was obtained by the addition of autotrophic and heterotrophic components which were affected by a variable inhibition term depending on irradiance level and acetate concentration.