Abstract
SUMMARY: Biological control is understood here in the classical sense, which is precisely defined by De Bach (1964) as ‘the action of parasites, predators or pathogens in maintaining another organism's population density at a lower average than would occur in their absence’. This account consists of a survey of the principal causes of disease in nematodes, with a summary of the efforts made to use certain pathogens in practise and a discussion of nematode pathology with reference to destruction of plant pathogenic nematodes.