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Seed samples of wheat and barley were collected in Nepal and Pakistan, from approximately 100 villages in each country. Nepal is said to be a Vavilovian 'centre of diversity' for barley and Pakistan for wheat. The samples were grown in controlled conditions at Bangor, N. Wales. The means, between plant variances and coefficients of variation for all characters, apart from awn length, were remarkably similar when comparisons were made both within and between the species of the two regions. Since the variation outside the previously defined centers of diversity was similar to that within them, the concept of centers of diversity must be reconsidered. We conclude that the amount of variation for quantitative characters is determined largely by natural selection. Variation of the major environmental variable, altitude, is equivalent in Nepal and Pakistan. Awn length was the only character to conform to Vavilovߣs description of variation: there was greater variation between barley plants from Nepal and between wheat plants from Pakistan. We conclude that domestication has reduced selection pressures in awn length thus allowing variation to be released and displayed in a Vavilovian fashion. It is argued that a species, within its 'centre of diversity', is particularly variable only for conspicuous qualitative characters whose variation is not limited by natural selection. In the absence of strong selection pressures, such variation can be maintained between populations by the fixation and loss of major genes. The barley collected from the rained agriculture of Pakistan. It is likely that wheat from Nepal is more disease resistant than wheat from Pakistan. In the light of these results, there seems to be little advantage in collecting plant germplasm from within centers of diversity in an attempt to capture the maximum amount of genetic variation. Collections should be made as widely as possible, and cover areas of great ecological (climatic and edaphic) or cultural variation. The maximum amount of variation for disease resistance is likely to occur in areas where the incidence of disease is greatest. [ABSTRACT FROM AUTHOR]