 Brian DonlevyProf. Bernard Quatermass | Prof. Bernard Quatermass |
 Richard WordsworthVictor Carroon | Victor Carroon |
 David King-WoodDr. Gordon Briscoe | Dr. Gordon Briscoe |
 Jack WarnerInspector Lomax | Inspector Lomax |
 Margia DeanJudith Carroon | Judith Carroon |
 Maurice KaufmannMarsh | Marsh |
| JJohn WynnDetective Sergeant Best | Detective Sergeant Best |
 Harold LangChristie | Christie |
 Lionel JeffriesBlake | Blake |
 Thora HirdRosie Wrigley | Rosie Wrigley |
 Sam KyddPolice Sergeant Questioning Rosie | Police Sergeant Questioning Rosie |
 Jane AsherLittle Girl (uncredited) | Little Girl (uncredited) |
 Toke TownleyThe Chemist (uncredited) | The Chemist (uncredited) |
 Gordon JacksonBBC TV producer | BBC TV producer |
 Margaret AndersonMaggie (uncredited) | Maggie (uncredited) |
 Eric CorrieMaggie's Boyfriend (uncredited) | Maggie's Boyfriend (uncredited) |
| HHenry B. LonghurstGeorge, Maggie's father (uncredited) | George, Maggie's father (uncredited) |
| EErnest HareCrash Site Fire Chief (uncredited) | Crash Site Fire Chief (uncredited) |
| MMichael GodfreyCrash Site Fireman (uncredited) | Crash Site Fireman (uncredited) |
 Marianne StoneCentral Clinic Nurse (uncredited) | Central Clinic Nurse (uncredited) |
 John KerrPhoto Lab Technician (uncredited) | Photo Lab Technician (uncredited) |
| BBartlett MullinsZookeeper (uncredited) | Zookeeper (uncredited) |
| MMayne LyntonZoo Superintendent (uncredited) | Zoo Superintendent (uncredited) |
| BBarry LoweNurse Tucker (uncredited) | Nurse Tucker (uncredited) |
| JJane AirdMrs. Lomax (uncredited) | Mrs. Lomax (uncredited) |
| MMolly GlessingMother at Zoo (uncredited) | Mother at Zoo (uncredited) |
| AArthur GrossTV Show Floor Director (uncredited) | TV Show Floor Director (uncredited) |
 Basil DignamSir Lionel Dean (uncredited) | Sir Lionel Dean (uncredited) |
 Donald GrayTV Program Announcer (uncredited) | TV Program Announcer (uncredited) |
| GGron DaviesCharles Greene (uncredited) | Charles Greene (uncredited) |
