Genetic diversity in agricultural systems relies on both the supply of diversity through varieties produced by breeding programs, and the demand for that diversity, through farmers' usage of varieties. Variety choice by farmers is demonstrated through the mix of varieties that is grown in a given region. In this paper, the conceptual issues relating to the supply of and demand for genetic diversity are explored. An empirical analysis of the varietal demand, based on the varieties grown in the Temora Shire in southern NSW over the post-War period, is undertaken. Changes over time in the choice of varieties by farmers are analysed, and some implications for genetic diversity are discussed.