To examine the role of kappa opioid receptors in memory formation, 2-day-old chicks were injected intracerebrally with either the endogenous opioid peptide dynorphin(1-13), the highly kappa selective agonist U-50,488 or the kappa selective antagonist nor-binaltorphimine (nor-BNI), given one-trial peck-avoidance training, and tested 24 h later. Dynorphin(1-13) impaired memory in a dose dependent manner at 24 h test. Injection of U-50,488 caused a biphasic dose-dependent effect on memory; low doses caused a trend toward enhanced memory and high doses caused significant impairment. Conversely, injection of low doses of nor-BNI caused a trend toward memory impairment, and higher doses caused significant memory enhancement. The results indicate that memory formation for one-trial peck-avoidance training may be modulated by kappa opioid receptor activity.