Clinical symptoms and performance were evaluated after shuttlebox‐trained miniature pigs received two 4400‐rad doses separated by time intervals of 10 − 4‐30 min. The doses were delivered to the head by 45‐MeV electrons from the AFRRI electron linear accelerator (LINAC). There was no significant difference in neurological symptons (Convulsions, coma, ataxia) or in performance after the second dose between animals that received the two doses 10 − 4or 0.3 min apart. As the time interval between doses was increased from 0.3 min, however, neurological symptoms declined and performance improved markedly after the second dose. When the doses were 30 min apart, the pigs showed no decrease in performance within the intial 30‐min postirradiation. It was concluded that more than physiochemical processes were involved in the increased radioresistance to the second dose of radiation.