One day after training mice to associate a specific context with an aversive stimulus, they were returned to the conditioned context. Fearful behaviour (time spent freezing) was measured in adult offspring of dams that received either saline (solid bars) or CBX (open bars) during pregnancy. n = 13 male saline, n = 10 male CBX, n = 6 male saline–tempol, n = 6 male CBX–tempol, n = 14 female saline, n = 5 female CBX, n = 5 female saline–tempol, n = 4 female CBX–tempol. *P < 0.05 CBX compared with saline; †P < 0.01 tempol compared with no tempol.