We would like to thank Dr Preece for his letter. He raises the issue that loss of symptomatic workers during follow up does not explain the absence of a decline in lung function in workers who worked with laboratory animals for more than four years, and concludes that lung function decline in short term employed workers is not sustained. We think that this interpretation of our data is somewhat overoptimistic and is based on the assumption that lung function changes are similar in those lost to follow up and those …