This report describes a method for the isolation of nucleic acid from a suspension of matured virus. Nucleic acid (DNA) was isolated from a prototype strain of adenovirus type 7 and a clinical isolate of adenovirus type 7. Instead of the usual method of ultracentifugation, a filtration method was applied to concentrate the virus rapidly and nucleic acid was then isolated by a standard phenol/chloroform/isoamyl-alcohol extraction procedure. The DNA was found to be sufficiently purified to generate a reproducible restriction endonuclease digestion pattern. The clinical isolate of adenovirus type 7 revealed loss of restriction site for the endonuclease HindIII when compared with the prototype strain.