NOVELTY - An integrated process for producing diesel fuel from biological material involves separating hydrocarbons of different chain length of Fischer-Tropsch paraffins of biological origin; mixing first hydrocarbon stream comprising 21C to greater than or equal to 100C hydrocarbons of the paraffins, and second hydrocarbon stream comprising fraction of 5-18C hydrocarbons by catalytic hydrodeoxygenation of biological hydrocarbons and fraction of 5-20C hydrocarbons of the paraffins; and fractionating the mixed hydrocarbon stream; and recovering middle distillate fraction.    USE - For producing diesel fuel from biological material; and for producing biological middle distillate fraction as an additive for improving the cetane value of a fuel, and for improving the cloud point and/or pour point of the fuel (claimed).    ADVANTAGE - The process provides a high-quality middle distillate fraction from various biological sources e.g. from by-products of the wood-processing industry; provides high quality paraffinic biological diesel fuel, free from aromatics, oxygen and sulfur; provides fuel which is superior in quality compared to both crude fossil based diesel fuel and FAME (fatty-acid methyl ester) bio-diesels; and provides a high grade diesel fuel from totally biological resources by the industrial integration of two separate processes for producing biological fuel where excessive cracking is avoided by the separation of hydrocarbons of essentially the same length; avoids unnecessary treating of the hydrocarbon streams.    DETAILED DESCRIPTION - An integrated process for producing diesel fuel from biological material involves separating hydrocarbons of different chain length of Fischer-Tropsch paraffins of biological origin; providing a first hydrocarbon stream comprising 21C to greater than or equal to 100C hydrocarbons of the paraffins treated by catalytic cracking/isomerization; providing a second hydrocarbon stream comprising a first fraction of predominantly 5-18C hydrocarbons by catalytic hydrodeoxygenation of biological hydrocarbons and a second fraction of 5-20C hydrocarbons of the paraffins; mixing the first and second hydrocarbon streams; fractionating the resulting mixed hydrocarbon stream; and recovering a middle distillate fraction. INDEPENDENT CLAIMS are included for the following:    (1) production of diesel fuel from purely biorenewable sources using lignocellulosic material involving lignocellulosic material is gasified and used to provide Fischer-Tropsch paraffins, which are separated into fractions of hydrocarbons of different chain length; a fraction comprising 21C to greater than or equal to 100C hydrocarbons of the Fischer-Tropsch paraffins is then cracked under isomerizing conditions to provide a first hydrocarbon stream; a first fraction comprising biological hydrocarbons which are hydrodeoxygenated to provide a predominantly 15-18C paraffin stream and a second fraction comprising 5-20C hydrocarbons of the Fischer-Tropsch paraffins which is optionally hydrodeoxygenated; are optionally isomerized under non-cracking conditions to provide a second hydrocarbon stream; the two streams are combined and fractionated, and a middle distillate fraction is recovered;    (2) a method for narrowing the chain length distribution of a Fischer-Tropsch derived diesel fuel involving combining Fischer-Tropsch derived 5-20C hydrocarbons with predominantly 15-18C hydrocarbons obtained by hydrodeoxygention of biological hydrocarbons to provide a hydrocarbon stream; combining this hydrocarbon stream with a Fischer-Tropsch derived hydrocarbon stream of 21C to greater than or equal to 100C hydrocarbons which is cracked under isomerizing conditions; fractionating the combined hydrocarbon stream; and recovering a fraction of 11-20C hydrocarbons; and    (3) a biological middle distillate fraction comprising 5-95% of a first hydrocarbon stream and 5-95% of a second hydrocarbon stream having predominantly 15-18C atoms.