Fantastic Voyage (1966)

Scientist Jan Benes (Jean Del Val), who knows the secret to keeping soldiers shrunken for an indefinite period, escapes from behind the Iron Curtain with the help of C.I.A. Agent Grant (Stephen Boyd). While being transferred, their motorcade is attacked. Benes strikes his head, causing a blood clot to form in his brain. Grant is ordered to accompany a group of scientists as they are miniaturized. They have one hour to get to Benes' brain, remove the clot, and get out.