A survey of the inhibitory effects of various plant polysaccharides on PCR amplification of a 974-bp section of rbcL in spinach revealed that most of the polysaccharides tested (arabinogalactan, carrageenan, dextran, gum guar, gum karaya, gum locust bean, inulin, mannan, pectin, starch and xylan) were not inhibitory. In contrast, two of the acidic polysaccharides (dextran sulfate and gum ghatti) were inhibitory. The addition of 0.5% Tween 20 reversed the inhibitory effects of gum ghatti (polysaccharide:DNA ratio of 500:1). The inhibitory effect of dextran sulfate (50:1) could be reversed by the addition of Tween 20 (0.25% or 0.5%), DMSO (5%) or polyethylene glycol 400 (5%), but none of these three additives were effective at a 100:1 ratio of dextran sulfate/DNA.