Rats were given 50 shuttle-box avoidance trials; between the 25th and 26th trials an interval was imposed, varying from 0 to 1.5 hr. in different groups. The number of avoidance responses on the last 25 trials declined from 0 to 1 hr., and then rose from 1 to 1.5 hr. The implications of these findings to the hypothesis of an incubation of anxiety are discussed. (PsycINFO Database Record (c) 2006 APA, all rights reserved)