The effect of prenatal stress was determined on exploration in situations that induce different levels of fear. Dams (12) were stressed by noise and light thrice weekly on an unpredictable basis throughout pregnancy, and 12 controls were left undisturbed. The time spent by different groups of their adult offspring of both sexes in exploration was assessed during 4 min in a plus maze; large, well-lit open field (1), and open field (2) after prior exposure to a small, dark holebox. Prenatal stress resulted in a significant reduction in the number of arm entries in the plus maze and amount of time spent in the open arms. Locomotion and rearing were also reduced in Open Field 1 and 2, but these activities and hole poking were unchanged in the holebox. It is concluded that prenatal stress renders the animal more fearful to a novel, intimidating environment, which may be expressed as a suppression of exploratory activity.