Four groups of rats were given brief, unsignalled, inescapable shocks in a shuttlebox at a rate of 1/20 sec [shock‐shock (S‐S) interval = 20 sec]. The four groups were exposed to limited avoidance intervals of either 18, 15, 10 or 5 sec, terminating contiguously with the S‐S interval. A response during this interval could postpone shock for 20 sec (R‐S interval = 20 sec). Responses prior to the avoidance interval had no programmed consequences, but additional responses during the R‐S interval could postpone shock for a further 20 sec from that response, thus enabling shock to be postponed indefinitely. Acquisition was rapid for groups with avoidance intervals of 18, 15 and 10 sec but somewhat slower for subjects with an avoidance interval of 5 sec. There was evidence of temporal patterns of responding for all groups which could readily be interpreted in terms of Anger's (1963) CA