A biological evaluation method for rational and simply evaluating biological harmfulness or usefulness of a great number of natural and artificial chemicals, foods, etc. This method comprises adding a known amount of 2'-deoxyguanosine (dG) to a solution containing a test substance (drug, pesticide, functional food, etc.), optionally applying UV light and/or adding active oxygen generator, then quantifying 8-hydroxy-2'-deoxyguanosine (8OHdG) in the solution, and evaluating the toxicity or usefulness of the test substance according to the 8OhdG content (a higher 8OhdG content indicates a higher harmfulness of the test substance while a lower 8OhdG content indicates a lower harmfulness or an usefulness thereof). The invention also provide an apparatus for advantageously performing said biological evaluation method and an antioxidant preservative solution to be used in this apparatus.