KATZENSTEIN, H. (1992). Direct Marketing. Macmillan.
Lua i Stíl Chicago (17ú heag.)KATZENSTEIN, Herbert. Direct Marketing. Macmillan, 1992.
Lua MLA (8ú heag.)KATZENSTEIN, Herbert. Direct Marketing. Macmillan, 1992.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.