The above hypothesis could be critically assessed using both theoretical and empirical approaches. From a theoretical perspective, optimal selection indices for maximising gains from selection for economic value can be derived if precise estimates are available for narrow sense heritability, additive genetic variance,and additive genetic correlations between cane yield,CCS, and other economically important traits (e.g.Henderson, 1975; White and Hodge, 1989). Some estimates of these parameters have been reported (e.g.review by Hogarth, 1987) and could be used for this purpose. However, most available estimates were obtained using small numbers of parents several decades ago, and there is arguably a case for obtaining accurate estimates for larger sets of modern parents.From an empirical approach, a breeding program could be conducted that places much greater selection pressure on CCS than cane yield, and generation-wise gains in economic value could be compared with existing practices.One factor, which could limit progress in a breeding program focusing on selection of very high CCS parents, could be that genes promoting extremely high CCS through effects on assimilate partitioning may have negative effects on cane yield. Genes that preferentially partition assimilates into storage at expense of stalk growth may conceivably lead to reduced cane yields. This would be observed as a negative genetic correlation between CCS and cane yield among those clones with very high CCS.However, determining whether this side effect presents a serious problem or not can only be ultimately determined via examining genetic correlations between CCS and cane yield among progeny developed from a high CCS breeding program, and ultimately from gains from selection for both CCS and cane yield. In the meantime, it would seem sensible that any such breeding program should also placesome concurrent selection pressure on cane yield to avoid impacts in this direction.