A standard rule-based system was used to evaluate the presence, accuracy, and completeness of main concepts in the connected speech of 20 non-brain-damaged adults and 20 adults with aphasia. Main concepts form a skeletal outline of the most important information (or "gist") in a message. The interjudge and intrajudge reliability of the main concept scoring system and the test-retest stability of scores were acceptable. The non-brain-damaged group produced significantly more Accurate/complete main concepts, and significantly fewer Accurate/incomplete, Inaccurate, and Absent main concepts than the group with aphasia. However, when the performance of individual subjects was evaluated, what best discriminated the performance of subjects with aphasia from that of non-brain-damaged subjects was not the number of main concepts they failed to mention but the accuracy and completeness of the main concepts they did produce. Measures of main concept production may be a clinically useful complement to other measures of communicative informativeness and efficiency.