Common white sugar was ashed in a muffle furnace under controlled heating at 450 degrees C. Together with these samples, sugar with added amounts of Pb and Cd (20, 50 micro g) was mineralized in the same furnace. Depending on the absolute amount of Pb and Cd present in the furnace, an increase in the 'blank' values of the unspiked sugar samples was found. The same effect was observed when reference material containing natural amounts of Pb and Cd (TORT-1, Lobster) was present in the furnace. Although the results strongly depend on the blank levels of the muffle furnace, cross contamination effects could be demonstrated for both elements. The investigations demonstrate, that at a temperature of 450 degrees C, both Cd and Pb are lost during ashing of samples. The type of matrix in a sample with high contents of Pb and Cd has no significant effect on the volatility of these elements. The vapor lost from a sample containing high amounts of Pb and Cd will falsify the concentration in low level samples present in the furnace.