During product development of a factor VIII concentrate (Dutch blood banks) the conversion from unsterilized to autoclaved freeze-drying buffer caused impaired product characteristics after severe dry heat treatment (80°C for 72 h). Analysis of the freeze-drying buffers showed the presence of fructose and glucose in heated buffers, resulting from hydrolysis of sucrose. The detrimental effect of glucose and fructose on solubility, yield of factor VIII and color of the heat-treated product was confirmed by freeze-drying and heating products spiked with increasing levels of these monosaccharides. The effect of the use of freeze-drying buffers autoclaved with and without sucrose was examined in two other factor VIII concentrates, S(8) and Z8 (Protein Fractionation Centre, Edinburgh, UK). If sucrose was present during autoclaving of the buffer, a slightly lower yield over freeze-drying and 80°C heat treatment was observed. Since glucose is present as a substrate in the medium for the host cells during cultivation of viruses, its potential effect on the 80°C heated product (Dutch blood banks) was examined during the validation study of the inactivation of HIV-1 and Sindbis. The cultivation cycles for the virus inolcula were simulated and residual glucose levels measured. In the supernatant medium of the host cell culture used for the propagation of Sindbis no residual glucose was found. Glucose however was found in the supernatant medium of the host cell culture for propagation of HIV-1, and therefore small molecular weight substances were removed from the actual HIV-1 inoculum by ultrafiltration. The study of the inactivation of both viruses during freeze-drying and 80°C heat treatment was subsequently carried out without complications.