A study was designed to validate the Navy Readability Indices (NRIs) in an individualized instructional system using the criteria of comprehension and learning time. Two hundred Navy enlisted personnel enrolled in a computer-managed technical training course were tested for both comprehension and learning-time-to-criterion on four programmed instructional modules. The subjects were divided into four groups having reading-ability grade levels of 9.3, 10.1, 10.8, and 11.7. The modules were classified by reading ability grade levels (9.1, 10.6, 11.3, and 12.5) using the NRIs. Results (which were supported by a replication) indicated that both readability and reading ability were significant predictors of comprehension and learning-time-to-criterion. In addition to validating the NRIs for programmed instructional materials, the study has implications for further research into the learning-time criterion for readability. (Author)