The assessment of emphysema in human lungs has traditionally been based on observations made on whole lung slices. These methods are inappropriate for the study of early emphysema, because as much as 75% of the alveolar wall surface area may have been lost by the time airspaces are visible to the naked eye. A new, automated image analysis system, the Fast Interval Processor (FIP), was used to measure airspace wall surface area per unit volume of lung tissue (AWUV). AWUV was measured on histological sections of lung tissue and expressed in mm2/mm3. The study sample consisted of resection specimens from 40 patients (32 men and 8 women whose ages ranged from 23-74 years). Histological sections from the inflated specimens were scanned using the FIP, and a mean AWUV value was calculated for each. The intra- and interobserver reproducibility of this method of measuring AWUV were examined. The results obtained using the FIP were also compared with those from an established image analysis system. The FIP is a fast, efficient technique which gave highly reproducible results comparable with those obtained with an established and much more time consuming measuring technique.