The effect of low temperature and controlled atmosphere (CA) storage on the degradation of cell membranes was investigated during postharvest senescence of broccoli flower buds. Broccoli ( Brassica oleracea L., Italica group, cultivars ‘Stolto’, ‘Commander’ and ‘Green Valiant’) heads were stored for 6 or 9 weeks at 1 °C under atmospheres containing nitrogen and 0% CO 2-20% O 2 (air) or 8.5% CO 2-2.5% O 2 (CA). During storage in air the phospholipid content decreased and the free sterol : phospholipid ratio increased. These changes were delayed under CA. The slight increase in the degree of unsaturation of the phospholipid fatty acids observed during storage in air was also delayed under CA. Storage had little influence on sterol content. The results show good correlation between phospholipid degradation, increase in sterol : phospholipid ratio and postharvest senescence of broccoli flower buds. The development of treatments which would stabilise the cell membranes would be an important approach which would go to the root of the problem of postharvest conservation of broccoli.