The decline of Globodera rostochiensis (Woll.) populations in two fields was 57% during the first and 40.3% during the second year of crop rotation in the absence of a potato crop in Co. Cork, Ireland. The decline was found to be due to both spontaneous hatch and in-egg mortality. Spontaneous hatch accounted for between 75.8 and 80.2% of the decline experienced during rotation. In-egg mortality was found to be responsible for a reduction of approximately 10% in the total number of viable eggs in both fields, and was positively correlated with soil temperature in the field. The number of culturable bacteria and the composition of the bacterial microflora in the cysts was found to change with increasing soil temperatures. The increase in cellulase-positive isolates reflected the effect of temperature on egg degradation.