TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The medium distillates are gasoils from primary distillation, vacuum distillation, thermal or catalytic cracking, and fuels from a Fischer-Tropsch process or fuels of a synthetic origin. The gasoline is gasolines deriving from catalytic processes and/or gasolines deriving from reforming processes. The gasoline derives from fluid bed FCC. In the hydroisomerization step a catalytic composition is used, where the catalytic composition comprises: (a) a carrier of an acid nature comprising a completely amorphous micro-mesoporous silica-alumina having a silicon dioxide/aluminum oxide molar ratio of 30-500, a surface area of greater than 500 m2/g, a pore volume of 0.3-1.3 ml/g, an average pore diameter of less than 40 Angstrom ; and (b) a metallic component comprising one or more metals of group VIII, possibly mixed with one or more metals of group VIB. The hydrodeoxygenation step is carried out at a pressure of 25-70 (preferably 30-50) bar, and at a temperature of 240-450 degrees C, preferably 270-430 degrees C. The component of a biological origin is obtained by a hydrodeoxygenation step, and optionally an isomerization step, where in the hydrodeoxygenation step the mixture of a biological origin is hydrodeoxygenated with hydrogen in the presence of a hydrodeoxygenation catalyst. The isomerization step is affected in the presence of hydrogen and a hydroisomerization catalyst. The carrier of an acid nature of the catalytic composition used in the hydroisomerization step comprises a silica-alumina having a silicon dioxide/aluminum oxide molar ratio of 50-300 and a porosity of 0.3-0.6 ml/g. The hydroisomerization step is carried out at a liquid hourly space velocity (LHSV) 0.5-2 hours-1 and with a hydrogen/hydrocarbon ratio of 200-1000 Nl/l. Preferred Components: The catalysts contain a carrier and one or more metals comprising metals of group VIII and group VIB. The metal or metals are palladium, platinum, nickel or from the pairs of metals nickel-molybdenum, nickel-tungsten, cobalt-molybdenum and cobalt-tungsten. The catalysts are previously sulfided. The catalyst is catalysts containing zeolites and/or metals of group VIII, and a carrier. The metal or metals of group VIII are platinum, palladium, nickel and cobalt.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The composition contains 20-95 (preferably 40-80) wt.% of gasoil component, 1-40 wt.% of gasoline component and 4-60 (preferably 20-60) wt.% of hydrocarbon component of a biological origin. In the composition, heavy gasolines from catalytic cracking processes (FCC) are used as such or desulfurized and/or heavy gasolines from reforming. The compositions additionally contains cold flow additives, detergents, lubricity improving additives, antifoam agents, cetane number improvers, antirust agents, antioxidants, antiwear agents and conductivity improvers. In the composition, before the hydrodeoxygenation step, the charge of a biological origin is treated in order to remove the content of alkaline and alkaline earth metals by means of adsorption or blandly acid washings. Preferred Components: The gasoil component comprises one or more medium distillates. The gasoil from catalytic cracking is a desulfurized gasoil fraction coming from fluid bed catalytic cracking (light cycle oil). The cuts used in the diesel component have undergone a hydrogenation treatment. The gasoline component is a gasoline characterized by a T95 (ASTM D86) not higher than 250 degrees C, preferably not higher than 240 degrees C. The gasoline has a density of 855-910 kg/m3. The gasoline component has a cloud point of lower than -40 degrees C. The gasoline component has a content of aromatic compounds of higher than 50 wt.%. The esters of fatty acids contained in the mixtures are triglycerides of fatty acids, where the hydrocarbon chain of the fatty acid contains 12-24C and is mono- or poly-unsaturated. The mixtures of a biological origin is: mixtures of a vegetable or animal origin; vegetable oils, vegetable fats, animal fats and/or fish oils; and sunflower oil, rape oil, canola oil, palm oil, soybean oil, hemp oil, olive oil, linseed oil, peanut oil, castor oil, mustard oil, coconut oil, Jatropha oil, Virola oil, fatty oils contained in the pulp of pine trees (tall oil), bacon, lard, tallow, milk fats, recycled oils or fats of the food industry, of both an animal and vegetable origin, and/or vegetable oils or fats deriving from plants selected by genetic manipulation. EXAMPLE - No suitable example given.