Electronic spirometry units were used to monitor lung transplantation recipients upon their return home. The data from 77 participants were used to develop methods to verify that the pulmonary function measurements, forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), were reliable and valid. The standard deviation was calculated for the best daily effort on consecutive days of home spirometry. An acceptable upper limit for the standard deviation, as the measure of day-to-day reliability, was 0.20 for FVC and 0.15 for FEV1. Validity was determined by examining the mean difference (bias) between the spirometry done in the pulmonary function laboratory and the home monitoring results. The clinic values were slightly higher, with an average difference of 0.15 for FVC and 0.12 for FEV1. Therefore, the home spirometry measurements have a high degree of reliability and validity and can now be used for early detection of serious complications.