Serial measurements of transfer factor of lung and its constituent components along with FVC and EFR25-75% were undertaken in 20 healthy nonsmoker adult males thrice on the same day. All the lung transfer components decreased as the day advanced, though reduction was statistically significant for Tlco and VA only. These changes were present in association with reduction in FVC and EFR25.75% indicating that patency of airways influences diffusion function of lung. Variations during the day are less than 7.4% and are hence unlikely to influence their diagnostic value, but serial estimation of these functions should preferably be carried out at the same time specially in the morning when these values are maximum.