Homoeopathy is a therapeutic system in which diseases are treated with substances, usually in extreme dilutions, which, when given to healthy individuals, produce the same symptoms as the disease being treated. Homoeopathy is an holistic method of treatment in that the whole organism is treated in an attempt to raise its level of resistance and stimulate its ability to throw off disease. In this respect it is well suited to the holistic concepts of biological agriculture. Because of the extreme dilution of the remedies they are relatively cheap, have little or no ecological side-effects and, on the whole, are harmless. This review introduces the basic principles of homoeopathy, discusses the experimental evidence for the efficacy of homoeopathic treatment of disease and considers its potential role in agriculture. The conclusion is that despite a great deal of experimental and clinical work there is only a little evidence to suggest that homoeopathy is effective. This is because of bad design, execution, reporting or failure to repeat experimental work and not necessarily because of the inefficacy of the system which has yet to be properly tested on a large enough scale. It is suggested that there is sufficient evidence to warrant the execution of well-designed, carefully-controlled experiments, particularly in naturally diseased organisms, to investigate the efficacy of homoeopathy further. Some of the experimental work already done suggests that homoeopathy may be of value in the treatment and prevention of diseases in crops as well as domestic animals.