Ninety-six rats were trained to criterion in a Y maze and then given differential treatment as to number (1, 5, 10) and duration (30, 60, 300 sec.) of unrewarded goalbox placements. Control Ss were run in the diagonal cells of the 3 x 3 design and differed from the experimental Ss only in that they were placed in a neutral box. A strong latent extinction effect was obtained for the dependent variables of speed of entering the goalbox (GT) and number of errors. The effect, strongest on the first correct trial in extinction, progressively weakened as extinction continued. The magnitude of the effect was influenced by number of placements, duration of individual placements, and the total exposure time, sometimes independently and sometimes in interaction depending on the response measure and the phase of extinction. Results are compared with those obtained by previous investigators and two theories of latent extinction are examined. Both theories, frustration and rg diminution, could accommodate the results pertaining to the effects of number and duration of placements. However rg theory has difficulty explaining the transitory nature of the effect.