Offspring of 30 gravid albino rats irradiated with 300-600 r of X-irradiation at conception ages of from 11 to 19 days, were trained in a Lashley III maze at age 50 days. They were significantly inferior to a control group in trials to criterion, errors and total time. Post-mortem examination showed multiple evidences of interference with neural development in the experimental animals. (PsycINFO Database Record (c) 2006 APA, all rights reserved)