This document is a report on the proceedings of an Expert Consultation on Biodeterioration of Cassava held at FAO Headquarters, Rome from 11 to 13 December 1991. The meeting was sponsored by FAO and cosponsored by the Rockefeller Foundation. It provided a forum for scientists to review the biochemistry associated with post-harvest deterioration of the cassava crop and to explore the possibility of applying modern molecular biology to develop varieties with superior storability. Cassava is a major subsistence crop for over 500 million people in developing countries. However, the rapid deterioration of fresh cassava roots after harvest is a severe problem to producers, consumers and marketers irrespective of the scale of operation. The roots begin to deteriorate as quickly as 24 hours after harvest and most cultivars deteriorate within two to three days. This situation is due to physiological deterioration which leads to substantial quantitative and qualitative post-harvest losses of the roots causing high production, processing and marketing risks. Current post-harvest management practices used to extend the storage life of cassava roots were reviewed and were considered either technically or economically unsuitable for most marketing needs. Although the mechanism involved in post-harvest deterioration has yet to be adequately elucidated, it was felt that the problem could be resolved considering that, when the crop is left unharvested, the roots could be "stored" on the plant successfully without deterioration for over one year. The genetic variability for post-harvest deterioration was reviewed and it was found that the evaluation method used was considered insufficiently precise to critically assess the trait. It was considered necessary to define and develop a screening assay to quantify post-harvest physiological deterioration in the available germplasm collection to determine genetic variability and stability.