Several studies have shown an improvement in the performance of motor skills following imagined performance of the skill, or "mental practice." One unresolved issue has centered on whether the effect being observed is in fact a practice effect. As one alternative, the effect may be a simple instance of planning when to use a skill, or deciding in advance what strategy to select. Alternatively, the possibility has been noted that mental practice may have its effects by influencing motivational factors, and not by exercising some component of the skill. A report is given of an experiment in which the procedures used by G. Nigro in 1983 to study imagined practice were replicated. The Nigro study reported that attempts to manipulate motivation make no difference in the effectiveness of imagined practice on dart throwing, whereas the content of the practice does. The results of that study appeared to eliminate motivation accounts and simultaneously to begin a specification of the relevant content of mental practice. A description is given of the experiment, designed both to replicate and extend Nigro's findings, and to examine the role of self-reported imagery ability using Nigro's procedure, a procedure that is apparently free of the confounding effects of motivation. (JD)