The permanent retention characteristic of imprinting has been supported both by naturalistic and experimental observation. If imprinting were simple conditioning, however, retention would be expected to show impairment following treatment, such as ECS (electroconvulsive shock), known to produce impaired retention in rats for various types of learning. 12 hr. Vantress chicks were imprinted, then administered 1 or a series of 9 sham ECS, or ECS at suprathreshold intensity for convulsion. At 48 hr. Ss were tested following parent and strange models, with order varied. There was much greater following of the parent model (retention), and even greater following occurred if initial testing was with the strange model. Retention was significantly impaired by a series, but not a single ECS.