The hydrotreatment of paraffinic Fischer-Tropsch wax fractions with a high congealing point (98 degrees C) was investigated in a flow reactor in the presence of a commercial sulfided NiMo/Al2O3 catalyst at temperatures ranging from 255 to 330 degrees C, at pressures of 30 and 60 bar, and at different hydrogen to liquid feed ratios. Three wax fractions of similar composition, but of different saybolt color, were used as feed which required different conditions to obtain a product with acceptable properties. In all cases, a pressure of 60 bar produced the best results and saybolt colors of better than +24 could be obtained at 330 degrees C from a feedstock with a color of -41 saybolt units. Minimal isomerization and hydrogenolysis of the wax was observed in the temperature range investigated.