Groups of aphasic patients and their spouses generated a series of communication situations that they felt were important in their day-to-day life. Using criteria to ensure that the situations were generalizable across people, times, and places, we reduced the number of situations to 36 and constructed an index that allowed the significant others of 11 recovering and 11 stable aphasic individuals to rate their partners' performance in the situations on two occasions 6 weeks apart. These data were then used to evaluate the psychometric properties of the Communicative Effectiveness Index (CETI) as a measure of change in functional communication ability. Further application of a generalization criterion reduced the final index to 16 situations. Results showed the CETI to be internally consistent and to have acceptable test-retest and interrater reliability. It was valid as a measure of functional communication according to the pattern of correlations found with other measures (Western Aphasia Battery, Speech Questionnaire, and global ratings). Finally, it was responsive to functionally important performance change between testings. Further research with the CETI and its usefulness for clinicians and researchers are discussed.