AbstractThis work formed part of a series of studies devised to investigate immunological markers which it was considered might reflect individual susceptibility to the development of coalworkers' pneumoconiosis and especially progressive massive fibrosis.Estimations of T and B lymphocytes and white blood cell counts (WBCC) were performed on blood samples from 324 coalworkers grouped according to radiographic category of pneumoconiosis, age, and smoking habits. A subgroup of 43 men was further screened for both humoral anti‐lung antibodies (ALA) and direct lymphocyte‐mediated cellular cytotoxicity (LMCC) towards human embryonic lung fibroblasts (HEL). In addition 673 serum samples obtained during a previous study of autoimmune factors in coalworkers were screened for humoral antibodies to HEL cells.The only correlation found between category of pneumoconiosis and alterations in WBCC, percentage or absolute numbers of lymphocytes, or the presence of anti‐lung antibodies was a decrease in a subgroup of T lymphocytes with increasing severity of pneumoconiosis. The major factor influencing these parameters in this study was the smoking status of the man. Smokers showed increased WBCC and lymphocyte numbers and a higher frequency of ALA and LMCC when compared with nonsm