Phytoestrogens are estrogen mimics produced mainly by leguminous plants, like clover, lucerne and soya beans, but also by some grasses and other plants. They are isoflavones and other plant phenols, bearing no resemblance to natural estrogens, but somewhat similar to non-steroidal synthetic estrogens, like diethylstilbestrol. Normally they have little ill effect on herbivores, but in large doses they can result in prolonged periods of estrus. It is suggested that when consumed by lactating cows, the estrogenic substance appears in their milk and transferred to the human consumer, on whom the effect could be similar to that of diethylstilbestrol - a substance with well substantiated atherogenic properties. This could be the explanation of the strong positive correlation between the consumption of mild and mortality from coronary disease reported in previous papers of the writer and other authors, and also of the differences between male and female mortality from coronary disease. When phytoestrogens are consumed directly in plants like soya beans, they appear to be correlated with cerebrovascular disease.