In order to mince lymph nodes for MAIC PCR–analysis, the Mixer Mill MM200 (RETSCH GmbH, Haan, Germany) was used with reusable tungsten carbide grinding beads. Some of unexpected PCR results indicated the carryover of DNA contamination among different samples. Hence, several decontamination procedures were used and the surface of steel and tungsten carbide beads was examined for remaining and intact DNA. Physical methods (three washes with distilled water, autoclaving and UV treatment) did not eliminate the DNA from both type of surface; this was also true for a procedure with Exonuclease III and the commercial DNA-removing kit DNAaway® (only used for steel beads). Chemical methods 0.25 % peracetic acid (PAA) (pH 5 and pH 7) and sodium hypochlorite (NaClO) (concentraction of active chlorine 4.7% or 5.4 %) removed DNA from tungsten carbide, but caused cracking of the surface of the beads. In conclusion, for grinding beads, the use of disposable material is suggested, as also employed for reagents and equipment in the PCR laboratory.