Approximately half of a worker population may benefit from the addition of a longitudinal comparison of their spirometry results, over only using annual comparisons with a cross-sectional LLN. The ATS recommendation of 15% for year-to-year changes appears to be essentially equivalent to a longitudinal LLN method based on the SEE. Therefore, a practical method for longitudinal interpretations is to establish a baseline value for a worker's FEV1 through several initial spirometric examinations. The FEV1 longitudinal LLN is calculated by taking 85% of this baseline value minus the expected decline over the time period based on the individual's age (e.g., for individuals older than 35 years at their initial examination, one approach is to use 30 mL/year times the number of years of follow-up). However, before any final classification is rendered, the data should be reviewed for stability. This analysis demonstrates that longitudinal spirometry adds sensitivity to spirometry screening efforts. The spirometry examinations should probably be performed annually in order to detect survey biases and determine the stability of the FEV1 measurements. If spirometry results indicate that someone has crossed either the longitudinal or the cross-sectional LLN, intervention activities should be initiated for that individual. As new data and studies become available, these suggested procedures will need to be revised-particularly estimates for the expected annual decline in FEV1.