This invention relates to a process for production of middle distillates having biodegradability properties. More particularly, this invention relates to a process for production of middle distillates produced from a mainly paraffinic synthetic crude which is produced by the reaction of CO and H.sub.2, typically by the Fischer-Tropsch (FT) process. The middle distillate produced according to the process of the invention may be a diesel fuel, having an aromatics content of less than 9%, as determined by the ASTM D 5186 or IP 391 test method. The paraffinic chains of the middle distillate may be predominantly isoparaffins.