Whole parasites or nucleic acids from these organisms can be immo bilized on filter supports, such as nylon or nitrocellulose. This allows many samples to be tested for the presence of a specific sequence by hybridization to a complementary DNA probe. In addition, the copy number of this sequence can be estimated under certain conditions. The different methods of application of material to filter give rise to the names of the different ways of blotting: dot blotting, slot blotting, and touch blotting. In dot blotting, the DNA is applied in solution to the filter via small circular wells of a manifold apparatus (1 ). Slot blotting is identical except that the wells of the manifold are elongated to form a slot. In touch blotting, DNA or whole organisms are applied manually to the filter. The resulting spots may not be as regular as using a manifold, but the results are as satisfactory.