We have studied the feasibility of using interactive computerized morphometric methods for the quantitation of septal thickness in the lung with the goal of introducing objective criteria for the diagnosis and grading of pulmonary fibrosis and edema. After reviewing available methods, we have decided in favor of linear intercept measurements of septal profiles which are limited to the tissue and therefore not affected by the level of lung inflation. Our method consisted in generating a graphic overlay of parallel lines over a real time video display of lung tissue. We had the options of measuring either uniformly oriented (random) or orthogonal intercepts. Randomly oriented intercepts (i.e., those with incidence angles ranging between 0 and 90 degrees) resulted in poor statistics because of excessive scattering of primary data; we resolved this difficulty by limiting the incident angle to the range of +/- 45 degrees from the normal to the septum at the point of sampling. This results in marked increase in consistency and reproducibility of the results with fewer measurements. Alternatively, we used intercepts measured over a line generated perpendicularly to the septal axis which approaches orthogonal thickness measurements. We found that both approaches yield acceptable results after as little as 50 measurements.