The increasing mortality among domestic fowls in this country has of recent years drawn attention to the possibility that worms and other parasites may be factors in the causation of certain poultry diseases. Heavy infestations with worms are frequently observed on farms where mortality is high and although it is rare that death can be directly attributed to the parasites, it is thought that they might be responsible for loss of condition in the birds, and for lowering their resistance to disease. On the other hand, equally heavy infestations may be found in apparently healthy birds and the few experiments which have been carried out to test the pathogenicity of certain common intestinal worms have not shown any marked effect on the health of the birds as a result of the infestation. Further work along these lines is however, necessary before the pathogenicity of helminths in poultry and their relation to disease is understood.