Twins with coal-workers' pneumoconiosis.

As the tuberculous hypothesis of coal-workers' progressive massive fibrosis (P.M.F.) is not so strongly held nowadays the possible importance of genetic factors should be explored. Twins with pneumoconiosis should provide helpful information. Details are given of two pairs of twins; one pair is considered to be monozygotic and the other dizygotic. Blood grouping, secretor state, and Rose Waaler reactions were carried out as the results may help in any comparison with twins with coal-workers' pneumoconiosis discovered elsewhere. The brothers resemble each other in having a similar type of pneumoconiosis. The monozygotic pair have a relatively benign type of pneumoconiosis with early P.M.F. which has remained unchanged for eight years; the dizygotic pair show a nodular type ofpneumoconiosis which has shown definite progression with an increase in the extent of P.M.F. As a younger brother of the dizygotic pair also has pneumoconiosis details are included.