To investigate the influence of physical structure on oxidative stability, mayonnaises enriched with 16% fish oil with three different droplet distributions were prepared. During storage at 20°C the concentration of free radicals (measured by electron spin resonance), the intensity of the fishy and rancid off-flavours (judged by sensory analysis) and the concentrations of several volatile oxidation compounds (measured by GC-MS) were lower in mayonnaise with large oil droplets in the initial stage of the storage period. As small droplets imply a large oil/water (o/w) interfacial area, the data support the theory that lipid oxidation in mayonnaise is initiated at the o/w interface. After 3-4 weeks' storage, the oxidative progress was almost equal in different mayonnaises. Oxidative propagation thus appears less dependent of interfacial area. The droplet size also influenced rheological properties, e.g. mayonnaises with small droplets had higher gel strength and a more rigid structure. Although small droplets enhance rheological properties and stabilise emulsions physically, the oxidative deterioration apparently starts earlier as the interfacial area increases. This ought to be considered in processing strategies for emulsified food products, notably those containing highly unsaturated lipids.