Compared the recall of messages composed of randomly selected digits under 2 conditions: uncertain length, in which Ss were uncertain of the length of the to-be-presented message; and certain length, in which Ss were informed of the length of the to-be-presented message. Recall with messages of uncertain length is poorer than with certain-length messages. This difference is maintained despite considerable practice. These and other results are interpreted in terms of 2 factors: proactive interference and the behavioral strategy employed by Ss. (PsycINFO Database Record (c) 2006 APA, all rights reserved)