The effect of snow cover on the overwinter breakdown of medium-textured soils in southwestern Saskatchewan was studied during the winter of 1967–1968. Where a continuous snow cover was provided artificially (with snow fencing), there was a decline in the percentage of soil particles < 1 mm in diameter from October to April, with a marked drop from February to March when the snowmelt was high. The percentage of fine soil aggregates in the unprotected field depended upon the amount of natural snow cover and the moistening effect of snowmelt which occurred from time to time. Where a snow cover was prevented artificially, surface drying occurred and the exposed soil layer became highly erosive, particularly during February and March when air temperatures fluctuated widely. The fact that this occurred on treatments where air circulation was permitted and not under polyethylene cover is interpreted as evidence of the importance of water loss by sublimation iii the process of deaggregation.