An analysis was made of potential differences in elasticities of substitution between agricultural inputs over time in different sectors of South African agricultural production. The elasticity of substitution between input pairs in South African agriculture has declined considerably from 1960-1972 to 1973-1985. Total agricultural production seems to have more flexibility in dealing with input price variation than either wheat or maize production as distinct sub-sectors. U.S. agriculture exhibits much more flexibility in dealing with especially machinery price variations. The relative rigidity of the South African agricultural production process may at least partially be attributed to present competitive structures.