A process for the preparation of detergents containing a relatively low amount of isoparaffins, involving separating a hydrocarbonaceous product stream from a Fischer-Tropsch process using a cobalt based catalyst and producing normally liquid and normally solid hydrocarbons into a light fraction boiling below an intermediate fraction having detergent hydrocarbons, an intermediate boiling fraction having detergent hydrocarbons and a heavy fraction boiling above the intermediate boiling fraction having detergent hydrocarbons, followed by conversion of the detergent hydrocarbons present in the intermediate boiling fraction into detergents, the Fischer-Tropsch process being carried out at a relatively high pressure.