Soil samples from paired 'old' and 'new' sugar cane soils from 6 contrasting sites in 3 climatically contrasting areas of North Queensland were analysed to identify changes in soil chemistry resulting from continuous sugar cane monoculture. The aim was to identify soil factors that may be associated with, or act as triggers to, the expression of sugar yield decline. It was found that there was no consistent effect of time under sugar monoculture on soil chemical properties across all sites, when either the distributions of properties through the soil profile, or property values at specific depths, were considered. However, marked effects were noted at some sites with respect to some soil properties, and the lack of consistent results across all sites may therefore be attributable to the inherent differences between the soils sampled. These effects were generally consistent with soil acidification.