Summary Mature green tomato fruit ( Lycopersicon esculentum L. cv. Caruso) were acclimated to cold temperatures and their physiological properties compared to chilled and ripening fruit. Spin labelling studies on isolated microsomal membranes showed shifts to higher breakpoint temperatures from the initial 11–12 °C in the spin label motion parameter vs. temperature plots for the chilled and ripened fruit membranes; breakpoint temperature for the acclimated fruit shifted upwards initially and decreased to 8 °C after 15 days of acclimation. No changes were observed in the average fluidity of the membranes. Energy of activation (Ea) for ATP hydrolysis at low temperatures (5–17.5 °C) increased for the three treatments; however, after 15 days the Ea for the acclimating membranes was lower than for the chilled and ripening membranes. Over the duration of storage and for fruit from all treatments, changes in the expression of membrane associated proteins were observed. No changes were observed in the relative proportions of membrane phospholipids or fatty acids. Ultrastructural studies indicated microvesiculation of the endoplasmic reticulum (ER) and disruption of the ER lamellae due to chilling. Acclimating cells showed «budding off» of larger membrane vesicles, which may constitute a «retailoring» process responsible for increased chilling tolerance.