Bacterial and artificial magnetic particles were modified using a polyamidoamine (PAMAM) dendrimer and outer shell amines determined. Bacterial magnetic particles were the most consistently modified. Transmission electron microscopic (TEM) analysis showed that the artificial magnetic particles were structurally damaged by the modification process including sonication. Furthermore, laser particle analysis of the magnetite also revealed damage. Small quantities of dendrimer-modified bacterial magnetic particles were used to extract DNA from blood. The efficiency of DNA recovery was consistently about 30 ng of DNA using 2-10 microg of dendrimer-modified bacterial magnetite. This technique was fully automated using newly developed liquid handling robots and bacterial magnetic particles.