Two radiographic methods of assessing pneumoconiosis were compared. Two chest X-rays, taken 5 years apart, were available for each of 381 coal miners (SIC-1211). The films were evaluated using a side by side comparison methods, or by isolated assessment of each individual film. Evaluations were performed by three experienced physicians, and for side by side comparisons, a trained lay reader was used. Compared to the independent method, the side by side procedure resulted in a lower proportion of regression, more progression with less variability, and more divergence. Interreader disagreement was higher for the independent method, but still exceeded 50 percent for the side by side method. Disagreement was very high between the lay reader and the physicians. With the side by side method, disease progression was greater in miners with category 1 pneumoconiosis on first X-ray compared to those with no disease. The appearance of the first X-ray did not affect progression judgments for the independent method. Both methods contained a geographic bias for disease progression, and both showed the same progression trends in relation to smoking history and years of underground mining. Film quality had no effect on the evaluations. The authors conclude that the side by side technique is the method of choice because it is more easily applied and more practical.