In 1961-62 a survey of respiratory symptoms in 2528 workers in flax mills in Northern Ireland and of dust levels in the mills was conducted. The workers were followed up in 1978, because recent developments suggested that an upturn in the industry was likely. Flax dust has an acute, reversible effect on the respiratory system, and byssinosis is a prescribed disease under the Industrial Injuries Act (1965). However, the follow-up study found no evidence of an effect on survival of either exposure to dust or byssinosis. The number of applications to compensation panels for assessment and certification of byssinosis has increased greatly in Northern Ireland. Although certification is independent of any subsequent common law claim by a worker for compensation on the grounds of disablement consequent on negligence by his employer, it must weight heavily in such a claim. About 50 common law claims have been settled out of court for large sums in Northern Ireland, and 950 claims are waiting to be heard. The future cost to the industry is estimated to be at least 16 million pounds. Since byssinosis appears not to cause excess mortality, it is unlikely to cause serious long-term morbidity. Although workers should be compensated for disablement due to negligence, in the absence of unequivocal evidence of disablement caused by byssinosis the financial settlements being reached in Northern Ireland seem unreasonable.