The focus of this paper is application of the concept of "sonority" to the study of aphasic speech. An assessment tool that is capable of examining sonority effects was developed and administered to a patient diagnosed to have progressive non-fluent aphasia. This tool successfully distinguished the performance of the patient from that of two normal (control) adults with different degrees of literacy. The results based on accuracy and latency measurements in the segmentation and production tasks revealed that the difficulty of the patient is likely to lie with the integration of segmental and prosodic information of words during articulatory planning stage. The need for developing similar tools in other Indian languages and using them along with standard language assessment procedures is emphasized. (Contains 1 note and 6 tables.)