Mixed fluorocarbon/hydrocarbon amphiphiles, the so-called molecular dowels, have previously been reported to strongly stabilize concentrated (90% w/v, i.e. 47% w/v) submicronic size perfluorooctyl bromide emulsions emulsified by egg yolk phospholipids. The dowel molecules, used in equimolar amounts with phospholipids, enable the preparation of emulsions with large-sized particles which are impossible to obtain with phospholipids alone. We report here that molecular dowels (C6F13C10H21, F6H10) also hinder droplet coalescence induced by mechanical stress in sterilized emulsions with average particle sizes ranging from ca 1 to 16 microns. In contrast, the addition of equimolar amounts of perfluorodecyl bromide was found to have little influence on these emulsions' resistance to mechanical stress. This is consistent with the view that mixed fluorocarbon/hydrocarbon dowels are held in the interfacial film and reinforce its cohesion with the fluorocarbon phase.