Standard measures of economic growth do not adequately reflect changes in aggregate welfare over time. Sustainable national income is therefore defined as Net National Product with adjustments for the degradation of renewable and non-renewable capital. Productivity loss rather than replacement cost is the most theoretically correct way to value resource depletion. Modified net product is estimated for the agriculture and forestry sectors of Zimbabwe by valuing the loss of forest stock and soil erosion. The results show that traditional measures overstate the value of the agricultural sector's product by approximately IO percent in 1989. It is argued that indicators of sustainable national income do not ensure sustainable development; as with all macroeconomic indicators, they do not account for distributional and equity issues which are at the crux of sustainable development, nor do they point to mechanisms which would ensure sustainable resource management. Indicators are therefore a necessary but not sufficient condition for the achievement of sustainable development.