- The random amplified polymorphic DNA (RAPD) technique is a simple method to detect DNA polymorphism. It is sensitive to reaction conditions. Small changes in the reactants' concentration cause variations in amplification products. Using DNA from Asparagus officianalis, Dactylis glomerata, Mercurialis annua and Escherichia coli, we examined variability in the amplification pattern associated with reaction constituents. An increase in the ratio of Taq DNA polymerase to DNA in the reaction increased the number of amplified fragments. Increasing the concentration of primer resulted in the amplification of low molecular weight DNA fragments, while lowering the concentration resulted in high molecular weight fragments. Subsets of amplified fragments required different concentrations of magnesium for their highest intensity. Mechanical shearing of DNA obtained by sonication led to reduction in amplification of a subset of products. Enzymatic fragmentation of DNA by restriction enzymes led to loss or gain of specific fragments, depending on the DNA, primer, and restriction enzyme. RAPD markers of pooled DNA of anonymous pedigree should be critically evaluated for frequent ‘false positive’ markers.