The purpose of this study was to validate the constructs that define the difficulty levels of prose-task processing. To accomplish this, this study investigated the extent to which variables from a previous study ( Mosenthal, 1996 ) on document processing influenced difficulty on 165 tasks drawn from the prose scales of five national, adult-literacy surveys. It was found that three process variables accounted for 78% of the variance when prose task difficulty was defined using level scores. The constructs within five levels are specified in terms of a hierarchy of processing difficulty and proficiency. The application of these levels for designing computer-adaptive testing and instruction programs is considered, as are applications for conducting prose research and interpreting literacy policy.