A study of byssinotics diagnosed in Great Britain between 1974 to 1980 inclusive and followed up until mid 1986 shows that there is a continued annual loss of FEV(1) after leaving contact with cotton dust over and above that found in the general population. This applies to both Grade I byssinotics and Grade II byssitiotic and Grade III byssinotics. There is a definite improvement on leaving the mill especially for non-smokers and ex-smokers but they do not revert to normal. Bronchitis is not an invariable component of bysinosis and it appears to be related more to smoking that, to dust exposure. Those who stopped working in cotton mills more than ten years before their first examination developed their symptoms at a significantly earlier age and after significantly fewer years of exposure to cotton dust than did those who (were working more recently in cotton mills. This tends to confirm that control of dust levels in cotton mills has improved.