Two experiments with hooded rats, in which activity level changes before runway trials are explored as an index of conditioned fear, are reported. Animals were dropped into a shock runway from an enclosed chamber where activity was monitored. Those that received shock in the runway showed a reliable decline in activity, significantly correlated with a reliable rise in running speed. When extinction trials were widely spaced (Exp. II), the activity-level measure accurately monitored both extinction and spontaneous recovery of fear. These results suggest the activity measure as a useful tool for investigation of fear in complex behavior.