Page 36 Exhibit 21 LIST OF SUBSIDIARIES Registrant - National Service Industries, Inc. Registrant owns all of the common stock of the following subsidiaries: State or Other Jurisdiction of Incorporation Subsidiary Principal Location or Organization Lithonia Lighting Mexico, S.A. de C.V. Monterrey, Nuevo Leon Mexico Lithonia Lighting Products Co. of Arizona Conyers, Georgia Arizona Lithonia Lighting Products Co. of Georgia Conyers, Georgia Georgia Lithonia Lighting Products Co. of Nevada Conyers, Georgia Nevada NSI Holdings, Inc. Montreal,Quebec,Canada Canada NSI Insurance (Bermuda) Ltd. Hamilton, Bermuda Bermuda NSI Leasing, Inc. Atlanta, Georgia Delaware Productos Lithonia Lighting de Mexico,S.A.de C.V. Monterrey, Nuevo Leon Mexico Lithonia Lighting Servicios, S.A. de C.V. Monterrey, Nuevo Leon Mexico Selig Company of Puerto Rico, Inc. Atlanta, Georgia Puerto Rico South Insulation Co., Inc. Atlanta, Georgia Texas I.A. Enterprises, Inc.which owns the stock of- Santa Clara, California California Keplime B.V. Bergen op Zoom, Holland Netherlands ZEP Europe B.V. which owns the stock of- Bergen op Zoom, Holland Netherlands ZEP FRANCE Nogent-le-Roi, France France Zep Industries S.A. Nogent-le-Roi, France France Resolve S.A. Nogent-le-Roi, France France Research Development Industries S.A. Nogent-le-Roi, France France Chemical Continental Industries S.A.R.L Nogent-le-Roi, France France Zep Italia S.r.l. Aprilia, Italy Italy ZEP Belgium S.A. Brussels, Belgium Belgium Research Development Industries S.A. Bern, Switzerland Switzerland Graham International B.V. Bergen op Zoom, Holland Netherlands Kem Europa B.V. Bergen op Zoom, Holland Netherlands Cerfact Europa B.V. Bergen op Zoom, Holland Netherlands Chemical Specialties B.V. Bergen op Zoom, Holland Netherlands The consolidated financial statements include the accounts of all subsidiaries.