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SUMMARY: Reversions to wild type occurred when conidia of a number of biochemically deficient mutants of Aspergillus niger were treated with DNA from the wild-type strain. No reversions or wild-type colonies were obtained when an equivalent number of conidia from deficient strains were either treated with the same DNA as the recipient, or were plated without any DNA treatment. Increase in the percentage of transformation was observed up to 6 μg./ml. of donor DNA. The transforming activity of the donor DNA was found to be inhibited by the action of u.v. radiation, heat and DNase. The frequency of transformation was low which could be attributed to the method of extraction of DNA which involved crushing of cells in the presence of alumina, possibly breaking the DNA into small fragments thus making it biologically less active.