A process for the preparation of detergents involving separating the hydrocarbonaceous product stream from a Fischer-Tropsch process producing normally liquid and normally solid hydrocarbons into a light fraction and one or more heavy fractions, hydrogenating at least part of the light fraction to convert unsaturated hydrocarbons and/or oxygenates into saturated hydrocarbons, distilling product thus obtained into at least one fraction comprising detergent hydrocarbons, dehydrogenating at least part of the detergent hydrocarbons to obtain a detergent hydrocarbon stream having mono-olefins and converting the mono-olefins into detergents. The invention further concerns a process for the preparation of detergents in which process a hydrogenated product, which is obtained according to the above process, is dehydrogenated to obtain a detergent hydrocarbon stream of mono-olefins, followed by conversion of the mono-olefins into detergents. Further, the invention relates to the combined production of detergents or detergent hydrocarbons and fuels from Fischer-Tropsch hydrocarbonaceous reaction product.