"Naalen" is the title character in the film, a ruthless black market kingpin whose wake inevitably follows a series of other crimes. How "Naalen" got his strange nickname will not be revealed here, but it can be hinted that it has a close connection to the precious and rare commodity he deals in his "business": insulin.
| Actor | Role |
|---|---|
 Ebbe RodeLorentzen, alias "Naalen" | Lorentzen, alias "Naalen" |
 Tove MaësGudrun, laboratorieassistent | Gudrun, laboratorieassistent |
 Gunnar LauringLarsen, kriminalkommissær | Larsen, kriminalkommissær |
 Hans-Henrik KrauseAlex Birk, stud. med. | Alex Birk, stud. med. |
 Louis Miehe-RenardOscar, Naalens håndlanger | Oscar, Naalens håndlanger |
 Jørn JeppesenStefan, Naalens håndlanger | Stefan, Naalens håndlanger |
 Sigrid Horne-RasmussenVærtinden | Værtinden |
 Ove SprogøeHelmer, kriminalassistent | Helmer, kriminalassistent |
 Tove BangFru Larsen | Fru Larsen |
 Lise ThomsenDanselærerinde | Danselærerinde |
| HHans Egede BudzLeder på insulinfabrikken | Leder på insulinfabrikken |
 Tavs NeiiendamLægen | Lægen |
 Aage Winther-JørgensenEn sortbørshaj | En sortbørshaj |
 Henry NielsenSkolepedellen | Skolepedellen |
 Karl Gustav Ahlefeldt1. filmoperatør | 1. filmoperatør |
 Gyrd Løfquist2. filmoperatør | 2. filmoperatør |
 Gunnar StrømvadEn laboratorieassistent | En laboratorieassistent |
 Gotha AndersenNot listed | Not listed |
 Axel StrøbyeNot listed | Not listed |